Rubber trolleys work to move people but promote little development potential due to lack of a permanent street presence. However, if street presence was improved, say with permanent, robust stations, on street markers indicating line alignment, real-time information and center lane boarding options then the gap could diminish, by how much I have no idea. Personally, I would ride a bus and rail trolley through downtown and what not.
Additionally, trolleys generally need to be free or extraordinarily inexpensive to use. Luckily, if a private trolley is operated it can be done so fairly inexpensively. If COTA operates a trolley, a public-private partnership could cover the fare-box fees.
Take a look at this bus, though. I think it's pretty neat and if there were both rear and front boarding, on both sides of the bus, it could work.
I do have to mention that a huge problem with High St. is the lack of street width. At least one lane of metered parking would have to be ditched and off-street public parking increased.
Another potential issue, and this may sound ridiculous, but pedi-cabs and cab drivers could file state and potentially federal complaints against a free trolley if it is ran by a public entity.
Oh as a note, someone was talking about implementation time-frame, bus purchases typically take over a year to complete. Buses are built to spec, so it's not a quick process.
Additional note, the new transportation bill, MAP-21, favors heavily increased discretionary funding for new BRT's and an inclusion of BRT's as core capacity (I think, as I read it).