There are really two distinct functions that happen when a set is cashed in. I haven't thought all the way through this but wanted to get it out for discussion but what if instead of the following spoils:
Escalating, Flat Rate, Nuclear, Zombie, No spoils
we broke them into two buckets (below), one for what troops you receive and one for what happens when a territory is part of a set.
Troop spoils:
Escalating, Flat Rate, None
Territ spoils matching:
Standard(+2 when owned); Nuclear; Zombie, None.
The thing that made me think of this is I think Escalating spoils with zombifying would be fricking awesome. Zombie on it's own is neat but nothing I'd play often but I think the combining of this with escalating would be very intriguing.