There is very few applications which can display the AI thumbnails. But all these applications (including ST Thumbnails Explorer (STTEX) v1.2.2260 and Adobe Inc. products) display the thumbnails not for all AI files.

It has very simple explanation. AI files of old versions (up to version 7) at all don't contain thumbnails. And version 7+ AI files can be without built-in thumbnails (for example, if its are exported from other applications which allow to turn off thumbnails creation).

Moreover we know cases when at incorrect installation of Adobe Illustrator 10 and/or others Adobe products, Illustrator 10 writes files in version below 7 (met 5.0 and 6.0) though a user selected saving in version 10!

Certainly having Ilustrator 7+ (or other products which may import these files and write in version 7+) these files can be converted to version 7+. However many individuals and companies has accumulated very much AI files of old versions and to convert manually is very toilfully.

Now we offer a partial palliative solution of the problem at least for those who has Illustrator 10+. (We outgo from the supposition that Ilustrator is installed correctly and creates files of that version what you select. The version of AI files is displayed in STTEX infotips for these files). It is ST AI Converter v1.3, the batch converter for all files which can be opened in Adobe Illustrator 10+ to AI files version 7-13(CS3). ST AI Converter (STAICONVERT) is freeware. Its usage does not required any registration. You may download (staiconv.zip, 102 KB) and try it right now.

Good news. ST Thumbnails Explorer 1.5 Beta can show magnificent (up to 600x600 pixels) thumbnails for AI and AIT files using CorelDRAW 12+ and/or Ghostscript. Ghostscript is free for end users, CorelDRAW is commercial.
With Ghostscript STTEX 1.5 Beta can display generated thumbnails for AI files v7-CS3 (the files v10-CS3 must be PDF-compatible). The next version (1.6) will be capable to display the generated thumbnails for AI files v3-CS3. Nevertheless PDF incompatible files v10-CS3 and AIT files will not be displayed (will be displayed the built-in thumbnails only).
With CorelDRAW 12-X4 the app can display all types of the AI (and AIT) files already now without any conversion and save the generated thumbnails to a database (disclaimer: unfortunately some separate files CorelDRAW engine is not capable to process). Please click here for details/last news.

Note.
•.ST AI Converter can be used for conversion of any files to AI files with built-in thumbnails. Of course, if these files may be opened in Adobe Illustrator.
•.ST AI Converter uses JavaScript engine implemented in Adobe Illustrator 10-CS3. Therefore it can be used on all platforms supported by Adobe Illustrator 10+ (for example, Apple Macintosh or UNIX).
•.You can use a similar script ST EPS Converter for conversion of any files to EPS files with built-in previews.

ST AI Converter v1.3 User's Guide

• Requirements

Adobe Illustrator 10+ should be installed.

• Installation scripts

• Unzip the archive staiconv.zip to temp folder and close Illustrator if it's launched.

• Copy all files with extension .js from temp folder to folder <Illustrator>\Presets\Scripts.

For example: if your copy Adobe Illustrator 10 is installed to
C:\Program Files\Adobe\Illustrator 10, copy the files SaveDocsInVersion7.js,
SaveDocsInVersion8.js, SaveDocsInVersion9.js, and SaveDocsInVersion10.js
from temp folder to C:\Program Files\Adobe\Illustrator 10\Presets\Scripts.

Note. If Adobe Illustrator CS2 is installed to C:\Program Files\Adobe\Illustrator CS2, copy the files SaveDocsInVersion8.js, SaveDocsInVersion9.js, SaveDocsInVersion10.js, SaveDocsInVersion11.js, and SaveDocsInVersion12.js from temp folder to C:\Program Files\Adobe\Illustrator CS2\Presets\Scripts.

• Copy the file AIVersConvert.aia from temp folder to folder
<Illustrator>\Presets\Action Sets.

Note. If Adobe Illustrator CS/CS2/CS3 is installed copy the file AIVersConvert.aia from temp folder to folder <Illustrator CS/CS2/CS3>\Presets\Actions accordingly.

• Script settings

• Launch Adobe Illustrator and open palette Actions (click in menu: Window|Actions).

• Click expanding button in the right upper corner of the palette and click
Load Actions...   

• In the Open File dialog select AIVersConvert.aia. It will add the Action Set with the name AIVersConvert to the Actions palette.    

• Select in the set AIVersConvert the appropriate action (ConvertToVersion_7 for conversion to AI v7 with built-in thumbnails, ConvertToVersion_8 for conversion to AI v8, etc.), and click the triangle at the left.    

Note. JavaScript for Adobe Illustrator CS+ cannot convert files to AI v7. If you select this action in Adobe Illustrator CS+, the files will be converted to AI v8.
Similarly, JavaScript for Adobe Illustrator 10 cannot convert files to AI v11+. If you select this action in Adobe Illustrator 10, the files will be converted to AI v10.

• Click expanding button and select in the popup menu Start Recording.    

• Click expanding button once again and select Insert Menu Item....    

• Click in the main menu File|Scripts|SaveDocsInVersion10  , and click Ok in the dialog Insert Menu Item....   

• Click button Stop Playing/Regording on the bottom this palette.

• Batch conversion

• Clear folders with processed files from files of types which don't opened in Illustrator.

• Select the string ConvertToVersion_10 in Actions palette and click Batch... in expanding button menu. Set up all parameters how its are set on screenshot.

• Click Choose in the Source group of the Batch dialog and select folder with files which should be converted. For process the subfolders, check Include All Subdirectories option.

Note. If you wish to process at once some thousands files (for example, a CD), Adobe Illustrator can lose stability. In this case will be reasonable to divide all files on groups for 200-300 files in everyone. Except it, is desirable the Illustrator relaunch after processing each group.

• Click Save As in the Errors group and select folder for Log Errors.txt file.

• Click Ok for start of the processing. All files from selected folder (and subfolders if you check Include All Subdirectories option) will be automatically open, processed, saved in the selected version and closed.

Note. If stability of Illistrator during execution of the script seems to you unacceptable, try set of the delay after opening a file before its write. For this purpose before run the script please click expanding button in a right upper corner of the Actions palette and click Playback Options. In the opened dialog set up Performance parameter to Pause for: x seconds, where x is the pause in seconds after opening a file prior to the beginning of its processing by script. We recommend values from 1 to 5 seconds.