We loved our stay at Pop! We just stayed there on our first night on our last trip to save money as our ressie for a DVC rental started on Sunday.
Anyway, Pop hasn't changed a bit (IMHO) since our original stay. Our kids still loved the grounds and they were very well kept up. The main pool (Hippy Dippy) was great, the food court was great and the kids just loved the icons and all of the funky stuff.
As you can see from my siggy, we have stayed just about everywhere except the Deluxe hotels. What I can tell you is that if you know you will sacrifice a little in room size and in room amenities and grounds amenities such as a pool slide or sit down restaurant, etc., and you are okay with that, then you will be fine. I would rather be able to go to Disney on a budget than not go at all but that's just me.
Pop is fun and if you go knowing not to expect too much from the room, then you will be fine.
Honestly, it's a different kind of stay because you get so much more from the fun and unique grounds. Where else are you going to find such huge icons, crazy and fun memorabilia, etc. I would go and think of it as a different, unique experience because it's a truly unique stay all it's own.
Just think of it this way - it's worth a shot at least once. If you don't like it, you won't have to do it again. Also, just one last thought - why not split your stay or stay at Pop for most of your vacation and then bump it up to mod or deluxe for your last two nights? Disney will transfer all your bags for you so it's really not difficult to make the switch and it will be something you can look forward to as well.
Good luck and hope this helps!