When I had a Bluebird the next logical upgrade was to a Top Hat. Same makers, same period. Difference is that the Bluebird keel is bolt-on and I had no way of checking the bolts without destructive testing. The Top Hat has internal ballast which is usually trouble free. Full headroom, etc.
However the level of fit-out and condition of rigging and sails and motor could make it an expensive buy if there is a lot of things to replace. Accepted wisdom is that unless you want a project, the best buy is usually the boat in excellent condition at a higher price.
What is the history of the Top Hat? Have you checked out
www.tophatyachts.com/ ?