When the Issaquah Highlands P&R was planned, the "perceived small community" was projected to be huge with both residential, retail, and business growth anticipated. Microsoft was even planning a huge complex up there at one time and the Sunset interchange with I-90 was built with that in mind (
...article from early 1998). Many projects have been curtailed, put on hold, eliminated, or cut back because of the economic slowdown. Someday, that growth will eventually materialize, I'd imagine.
Right now, I don't believe there is a direct bus from that P&R to downtown Bellevue. I know such a route was planned at one time. You'd have to make one transfer currently.
Here's how it "operates" (bays that you'd use for the route chosen --pay as you enter):
Issaquah Highlands P&R boarding locations
edit: I stand corrected. The Sound Transit
route 555 in the morning and 556 in the afternoon will be direct to downtown Bellevue. From downtown Bellevue, 556 in the morning and 555 in the afternoon.