You probably won't be able to feel too much increase anyways, as the engine makes only 88 HP. But, you can:
1. replace big and nasty air box with cone-shaped air filter; there aren't too many modified escorts on yards (if you modify and get crash, you will take anything usable out) but you could get the intake from 1.8 escorts.
2. ? I can't think of anything else that would increase performance very easily.
3. Speakers - if you see any lincolns town cars, or similar, you could swap speakers. You may have to do a little drilling in the door, and play with the rear ones, but it is definitely worth it.
3. Side skirts - looks better
4. wind deflectors that you could stick to front door - looks better, saw them at my local yard
5. rims if you can get a good deal on some aluminum ones
6. fuel injectors if yours are older and you see some 40000 miles escort completely smashed with injectors intact (also spotted at local jard here)