I felt that I was in a similar quandary for a few months with my '85 Miyata 210.
I was more concerned with the quality of the wheels I had on the bike, since the front hub was pretty worn out.
In the end, I decided to stick it out with the 27s since my Paselas were working out just fine and were in good shape, replaced the cone-nuts on the front hub (which sorta helped), and got a great N+1 with 700c Mavic rims. Just put Panaracer Pasela 28s on them.
Now from time-to-time, I just think about swapping over the whole wheelset. Nice to have the option....
