Credit score/new car options?

I will be buying a new car within the next two months; I have paid off my credit card debts, precious auto loans, and have been paying student loans and all bills on time for years, but my credit score ranges from 687 (Equifax) to 654 (Transunion). This is up from the lower 620 range from when I had a higher balance on cards, but not where I had hoped it would be carrying less than 30% balance. Anyway, I have enough to purchase the new Prius I want outright; I could pay for it in cash, but my hopes were to get a three year loan, and pay it off in that time frame to continually build my credit. My concern is that with my current credit score, I will be relegated to a high interest rate and end up paying much more in interest. Is that interest worth the bump in the credit score I might receive for the 3 year loan, as I imagine a larger down payment would be necessary (again, not an issue fortunately) and would it be a smarter long term move to still finance the car? My longer plan is to then purchase a house with the improved credit score after the car is paid off and my credit bounces back from that payoff, as 650s will not secure a realistic mortgage rate for me.

Read more: Credit score/new car options?