IMO, the priority order for spending excess coin would usually be:
1) Scout. Even if you can't complete the provinces, keep the scout busy
2) Upgrades and new productions
3) Basic Goods, unfortunately. It's expensive, but better to spend the coins than lose collection
4) KP. Very very cautiously. The thing about KP is that soon our Ancient Wonders will start adding score - each KP equals one point. So, try to avoid buying KP unless you're going to put it into a Wonder. The costs increase with every purchase, and eventually add up - high and fast!!
These recommendations are based on my personal goals - growing as quickly as possible. Ciao and good luck!