Hi Gail,
Not many new coffee shops there unless you count Northland shopping centre. There's a thought, using the coffee standard to determine an up and coming suburb.
Yes, you're right Preston is pretty cheap, especially compared to Heidelberg and Thornbury but watchout for low rental demand.
I knew someone who had an IP there vacant for several months.
I like Coburg more because it adjoins up and coming Brunswick and is still reasonably priced. Sydney road is also very busy, especially on weekends.
Cheers.