OK, I can reproduce and have a fix.
The sidebar engine by default does NOT scale for custom DPI. There is a parameter that you can add to tell it to scale this gadget. When you do that, the text shows properly now (and the gadget gets larger).
1 - Close the gadget.
2 - Open "C:\Users\<username>\Local\Microsoft\Windows Sidebar\HWiNFOMonitor.gadget\gadget.xml" using a text editor like notepad.
3 - Add "<autoscaleDPI>true</autoscaleDPI>" after line 20. Save and close the file.
4 - Open the gadget
Here are the details on where that line gets added:
Code:
<host name="sidebar">
<base type="HTML" apiVersion="1.0.0.0" src="gadget.html" />
<permissions>Full</permissions>
<platform minPlatformVersion="1.0"/>
<defaultImage src="icon.png" />
<autoscaleDPI>true</autoscaleDPI>
</host>
Let me know how you make out.