The new territory would (and did in OTL) carry the risk of overextension, but it was a rich region populated mainly by Greeks, and as such would increase revenues and provide a fair amount of manpower.
Considering the nonthreatening situation in Bulgaria (I forgot that kaloyan was already dead

) I'd imagine Michael and Theodore would immediately attack each other in traditional Byzantine style, to decide who would become
The Emperor.
They'd probably entice foreign powers (mainly Serbia, Bulgaria) to support them, with promises of land or religious concessions.
At the same time, though, the Seljuks are doing very well; IIRC they have already seized (or are about to) ports on both the Black and Mediterranean seas. Removing all of those men from Byzantine Anatolia at such a time may prove to be a mistake...