There are reasons why SGX appeals to people -- it's uniqueness, part of being the only true "all-in-one" PCE solution, looks, etc. etc.
However, if you just want it for playability sake, you're better off just modding the TG-16 & getting an arcade card pro. Then you can play everything PCE/TG-16 but the 5 SuperGrafx titles.
And if you break down those 5 SGX titles a bit further, only 3 are exclusive to the console -Aldynes, Granzort, BattleAce - and only Aldynes is supposed to be great (I've only tried Battle Ace, and it's okay, but not a real keeper IMO). In addition, if you do mod the Supergrafx, Aldynes is the one that's supposedly negatively affected by the mod... (though I just don't get that why that'd be the case if it was properly modded... It doesn't make sense, logic-gate wise.. anyway...).
As for the other 2 titles - 1941 & GnG - there are other "arcade-perfect" ports out there, so I personally don't see the extra incentive getting the SGX just for them, at least for sole sake of just playing them.
For me, after finding out that I didn't care too much the SGX library, I sold mine off to someone who'd get more enjoyment out of it than myself - to mike here, actually.