I'd love to see a set incorporate the footy parks in some way, say have a 'hometown hero' or 'crowd pleaser' clearcut on top of a birds-eye shot of each homeground. Could be a bit busy, but should be a styly way to do it.
In terms of honouring older players, I always enjoyed the Dally M Distinctions subset that Dynamic did back for its Extreme set, and its really a style of set that Select never bothered to mine. I agree there are a lot of stat orientated themes - 100 Try Club, Offload Kings, Line-break masters, one club career, etc - that have either never been touched or not since Dynamic.
I think there's always a place for rookie inserts, but Select went overboard with that huge 2011 Champions set and then this year's Rated Rookies, and were too slow to give them cards. Too many players, too much repetition and too many players who weren't actual rookies. I wonder if the NRL would ever allow a small Toyota Cup Prospects set...