Basically I want to buy another Mac – can be laptop or desktop – for general homework/wp/spreadsheet work

I would say something less than 5 years old

Any particular models I should seek out or avoid?

Pricing wise the older macbooks with plastic casing will be the cheapest so you could get a good buy there.

I would look at a macbook pro though, one of the two/three year old ones before the i5 came in.

Any MacMini’s about ? These would probably be the best value and you don’t need the high quality screen of an iMac for your usage nor the portability of a laptop.