No, they're really really really not. While not as bad as the Olmecs, they are a civilizatioh still shrouded in legends of which we actually know relatively little. Their "empire" is also more in the nature of a sphere of cultural influence than an actual empire - many of those cities belonged to other groups (read: Maya) but were heavily influenced by Toltec culture, for example.
Or, in civ terms, a lot of those areas had heavy Toltec loyalty pressure, but most of them never actually flipped.
i'd rank them fairly low on the priority list (but still far above Xicallanca); certainly the Purépecha and Zapotec are higher priority.
My view for Mesoamerican priorities:
0th tier (already here): Maya, Aztec.
1st tier (deserve representation, space permitting): Major civilizations extent around the time of conquest ): Purépecha, Zapotec and Mixtec, in that order
2nd tier (not that essential, but could be nice): assorted smaller, less organized groups: Chichimecan tribes, etc.
3rd tier (information likely insufficent to include, but would be nice): cool classic and post-classic empires we know only legends about: Toltecs.
4th tier (mosty useful if relevant scenarios are made): major offshots of the major civilizations extent c. The conquest: Highland Mayans, Tlaxcalla, etc
5th tier (Really no good reason) ; minor and trivial offshots of larger civs: Xicallanca
6th tier (not happening except as city state) civilization of which we only have assorted archaeological traces: Olmecs.
Seeing as we'd be lucky to get even one first tier civ into the game, let alone all three, second tier is a very remote chance at best, and beyond that...lol