Like most veteran player, I use to have many leftover:
mordian guard that I used as commisar when I began playing
2 or 3 of those that I bought 'cause they where cool
half a space marine army doing nothing
this ugly tank that I should stripped, but we all know that I will not.
you get the idear...
I tried to motivate myself to paint all those model and failed. The 97th imperal guard is less cool to paint, no matter how you put it.
and then...
I will trade all those things (with dakka trade forum, bartertown, and some friends), for a new army, with this little rule:
The only thing I have the right to buy for this new army is the codex.
This should be fun and motivating.