If you can afford the extra money I would sure go for the addition of a plunge base.
I have a pair of 690's and have the plunge base and D-handle to exchange bases with. Unlike the guys at Rockler I would say most of my routing is done with the plunge base followed by the D-handle then last would be the std. base.
I have a dedicated plunge router in a table with the springs out, so if you want to count that then the plunge routers are in use 70% of the time.
A lot of project take extra effort when using a std. base, you need a starting hole because you can't plunge, things like this also take extra time. Even making several passes is easier with a plunge router, you set the pole stop at the ending depth then plunge to less then that make a pass, come back and plunge a little deeper etc. On fixed base routers you will want to turn the router off to readjust the depth each time.....
I think everyone should have a plunge router but then that's just me. I started with a sear fixed base and moved up a lot of years later and wondered why I wanted so long.