I think the most important point to "Imasara Town" is Masara Town na koto. "What kind of a Pallet Town thing is that?" -> "What kinda noob talk is that?", since Pallet Town is the starting town in the 1st Gen games. The added "I" at the beginning seems to be a pun on the word 今更 (imasara), although I honestly don't get what that does here.

My Japanese blows, but you might be able to glean more complete information from these links:

https://www49.atwiki.jp/aniwotawiki/pages/27052.html
https://wikiwiki.jp/boudai/イマサラタウン