As a Realtor who services the Lawrenceville area, I would agree with your Realtor. There are some areas in Lawrenceville that would likely be better for Resale and others that, well, might not.
The historic district is getting a major overhaul in the next few years, so developments that are close to that should see a big bump. The changes will take several years however, so unless you're willing to wait 5 to 10 years, then I would just buy what you want.
I know where Oakland Downs is, but I don't know where the other one is. In general, if you are buying a townhome in Lawrenceville, you want to be as close to 120, 20, Sugarloaf or Old Norcross as possible. Those are your main thoroughfares. I don't like Townhomes in Lawrenceville, simply because 9 times out of 10 you can find a single family home for the same price. Townhomes in this area are stagnating in many cases, especially those just north/east of historic Lawrenceville.