[Van down by the river]

Sorry for the delay robbyville in my reply, I did one a few days ago and deleted it by accident.

I tried to verify which is stronger glass or acrylic, results seem highly dependent on the parameters of the test.

Tag on all you want...

As far as the Windex goes, it depends on how cloudy/opaque the acrylic has become. Try buffing an area not viewable like the top to see if the hazyness improves. If it's a custom built tank it's probably a better acrylic, and can take the buffing. If it's an old Seaclear tank it may craze easily if you try to buff it, again test a spot before you work on a main viewing area.

The acrylic cleaners can be bought from acrylic fabricators and suppliers listed under Plastics in the Yellow Pages.
Also Coralife makes a Acrylic buffer polisher spray that is non toxic (but for use on the outside of your aquarium). It is available at most Aquarium shops. KE should have it.

For the brushes, only use brushes "recommended for acrylic use" . Hagen brushes I find to be quite course and Prefer "LEE'S" Brand brushes. The acrylic one has a blue handle and a white brush head. They are very soft and work well. I'll mention the Quickwipes again as they are also very useful for hard to get places and cleaning pipes, powerheads.
Again most larger stores should carry them.

Rainbow lifegard/Pentair Aquatics has a scratch/buff kit.
If you have a electric buffer you can get the proper wheel and "cut" wax at
Acklands. You'd have do a fair amount of buffing to make the commercial equipment purchase worth it.
For small jobs you could use a dremel tool.

small scratches are easy, and most large deep scratches can be removed.
it takes some practice, and like anything you will improve with time and experience. If the scratches are very deep sometimes there will be a slight visual distortion left over but not always.

the soft quickwipes and brushes will get the algae within the scratch.
Teflon scrapers can be used with care.

The grade of acrylic will be hard to determine. If the tank is too cheap ask about the material, generally American made is a safe bet. I was told they are all the same but after fabrication it became evident that this was not the case.

Just remember when buying your new tank shop around take the time to do it