Providing hi-res textures to replace the in-game ones for your levels: Good.
Relying on a feature added by emulators, making your level unplayable on real hardware (or other emulators): Bad.
If your texture is just way too huge, feel free to provide hi-res texture packs (in fact please do), but please insert a scaled-down version in the game. Not everyone can use those packs.
In theory the number of textures you can use at once should be limited only by available RAM and fill rate, and IIRC the importer extends level data into the Expansion Pak memory, so you should have plenty...
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