I used a walk-through-walls cheat code to test the area around the circus tent. Basicly, most of the right side of the tent is glitchy. If you go farther rightwards or downwards, however, there won't be glitchy dialogue. I tested this area with autofire L at 30 Hz for 100.000 frames and didn't see any glitched text.
Edit:
http://img534.imageshack.us/img534/2329/fullmapsmall.png
* Glitched text spots are often located where there's a cross of map transition lines. There is no such cross at the circus tent, though. The spot there is also significantly larger.
* There are two spots I found so far that will always bring up glitched text. One of them acts very glitchy and will often result in a game break. (located in the north of Onett)
Edit:
I took pirohiko's TAS and modified it a bit. I only bought one skip sandwich and got another one from the trash can in Threed. I go directly to the circus tent to try my luck.
http://dehacked.2y.net/microstorage.php/info/547016345/EarthBound%20pirohiko%2C%20modified%20mugg.smv
I like this outcome, though it's useless...
On another note:
This glitch should be tested on the real console!
The glitch messages have differed between snes9x 1.43 and 1.51.