There's old downtown McKinney and Frisco....
I also like downtown Grapevine, but that's a little further than Plano.
I think old downtown Lewisville and Carollton, and Coppell may also stage comebacks.
Carrollton and Lewisville now have DART light rail service and I expect that to be a boon
to downtown living. Coppell expects DART rail stop and if that happens I think it will be a boon
to revitalization of that area....but plans are yet to be seen for that.
Some of these types of homes will be listed here, but there may be some outside of walking distance.
I would probably like to know more about what kind of shopping you expect and what price range you want to target, as well as if there is a specific draw to Plano (like work). Another area you might like, but maybe have less downtown feel is someplace in East Dallas east of I75....M-Street, Lakewood, Casa Linda, Hollywood Heights type areas.... you can read some about this area here:
Keller Williams Realty