You might want to try editing the font size. Starting with iTunes 10, font sizes are stored in a plist file (XML, text) at (assuming you use the English version)
($INSTALLDIR)iTunes.Resourcesen.lprojTextStyles.plist
There are quite a few fonts in there, and I don't know which one would change the Device summary page.
For example, you can change the List Contents (and source list) font by editing this part of the TextStyles.plist file:
<dict>
<key>- loc hint -</key>
<string>List Contents (Small)</string>
<key>font</key>
<string>Segoe UI</string>
<key>size</key>
<integer>8</integer>
<key>xp-font</key>
<string>Tahoma</string>
<key>xp-size</key>
<integer>8</integer>
</dict>
You want to change the "integer" value after the "size" key. e.g. to change the current font size (8) to 12:
<dict>
<key>- loc hint -</key>
<string>List Contents (Small)</string>
<key>font</key>
<string>Segoe UI</string>
<key>size</key>
<integer>12</integer>
<key>xp-font</key>
<string>Tahoma</string>
<key>xp-size</key>
<integer>8</integer>
</dict>
I haven't figured out what changing "xp-size" key does.
I've just updated my iTunes font size editor program to work with iTunes 10, but I don't know if it'll help on the device summary page or not.
http://www.pobox.com/~teridon/ituneshacks/index.html
The forum TOS requires me to say: "I may receive some form of compensation, financial or otherwise, from my recommendation or link" because I have a paypal donation link on my webpage and in the program, but the program is free (donation totally optional).