The US space program continuing to receive north of 4.5% of the Federal budget would almost certainly see a major (>20 person) outpost in LEO by the end of the 80s, a moon base (perhaps small, only 3-6 people to start) growing out of ALES and LESA, a fully reusable Space Shuttle from the beginning with no manned spaceflight "gap" as Apollo flies until Shuttle enters service, and a Mars landing in the 80s.
Larger infrastructure projects like launch loops or such could become feasible to investigate in practice thanks to the required throughput to space, though space elevators and such remain impossible from a materials perspective.
I have to say, though, that it'd be a pretty serious waste of funds. That'd be a continuing budget for NASA and spaceflight greater than the interstate highway program. One of those benefits almost every American directly, the other only does so indirectly and to a much lower extent. Such a proposition is one of the times you'd find me in the awkward position of agreeing with William Proxmire: cut the budget.