Work around
Some launchers can use more that 7 homescreens but do not have sense widgets.
And as started before, LauncherPro has some sense style wigdets.
I use LauncherProPlus with 7 homescreens, so if in the future I require more homescreens, I can just tap the red android on my main homescreen to quickly switch to original sense set-up. You could use it the other way around, with sense as your main launcher and LauncherPro as your secondary launcher., giving you a maximum of 14 homescreens.
Unfortunately I can not remember if LauncherPro (free market version) has the option I am about to describe, you would have to try it.
To set this up, you would need LauncherPro (possibly paid version LauncherProPlus), Desktop VisualizeR (free market app) and a .png image of your choice (in my case, the red android) copied to you sdcard.
Set-up using sense launcher
After installing Desktop VisualizeR and LauncherPro, set sense as the default launcher for when you press your home button.
In sense launcher. Long press a homescreen and choose "Widget" under the "Add items to Home" section.
Choose the size of Desktop VisualizeR widget you like.
Click "Select Icon" and pick "Image File". Find the image you wish to use.
Back on the Desktop VisualizeR menu screen click "Select Action", then "Other", then "Activities". Wait while LauncherPro compiles the list. Scroll down to the first "HTC sense" submenu and choose "HTC Sense/ com.htc.launcher.Launcher".
The other options I chose in Desktop VisaulizeR were:
"Label" = None, just tap the "Clear" button.
"Label Color" = Not used so ignored.
"Touch Effect" = None, the available colours do not suit my theme.
This how both launchers main homescreens look for me.
Sense Launcher
LauncherProPlus