Honest advice here - dont sell if you are just down on collecting at the moment. Pack them away for a while and once you are back on an even keep reconsider. If you still are not committed then you could sell but you may find it was just a bit of a dip. And selling now would be disappointing.
Unfortunately I really think a lot of the blind bag sets and waves have taken a dip in the last few months. Wave 2 is still commanding but the rest not so much
Wave 1 - $5-5 ($25 for pink TS)
Wave 2 - $12-25 depending on which one (retail for those which have since had a release elsewhere)
Wave 3 - $5-6
Wave 4 - retail
Wave 5 - retail
Wave 6 - retail
Wave 7 - retail
Wave 8 - retail
Wave 9 - retail
Wave 10 - retail
Wave 11 - retail
Wave 12 - retail
The exception to the rule are specials such as the W5 Princesses and W7 Wonderbolts. Any special which is not sold in another set/release. They tend to rule twice the value of the rest of the wave.
PVC Sets:
Apple Family Set - $16
Class of Cutie Marks Set - retail
Cloudsdale Set - retail
Daring Pony Story Set - retail
Elements of Harmony Set - retail
Friendship Celebration Collection - retail
Pinkie Pie & Friends Mini Collection - retail
Pony Friends Forever Collection - retail
Pony Rainbow Collection - retail
Pony Wedding Set - $25
Ponyville Newsmaker Set - retail
Rainbow Pony Favorite Set - retail
Soaring Pegasus Set - retail
Spa Pony Set - retail
Toys R Us Collector Set - $45