First of all, let me say that I can't imagine this corridor to be developed without a multi-use trail. This is a unique opportunity to create the first east-west non-motorized trail in Salt Lake proper. Being a daily bicycle commuter, I notice that non-motorized bike trails are one thing in which SLC is lagging way behind most of the other cities that strive to be more bike friendly (Portland, Seattle, Denver, Boise). Bike lanes are great for experienced commuters but non-motorized trails will attract people that are not comfortable being a few feet from a ton of steel with sometimes unpredictable line of travel (the streetcar being on rails at least is more predictable ;-) ).
That being said, I see the trail as the focus point and the central part of the corridor, with amenities built around it as conditions allow. I would hope that the trail goes in first with whatever money is (hopefully) left from the streetcar construction (BTW the trail is also transportation project, it's not a beautification - it will have an important function in moving people on bikes and on foot from one destination to another). Then as funding allows, in 2013 or whenever, do the actual beautification - landscaping, street art, etc.
I personally live a few miles from the corridor, so, I will only use the trail for transportation the same way as a resident of Sandy uses Foothill Blvd. to drive to the Research Park. So, similarly to the Foothill commuter, who probably does not care much about amenities around Foothill, I am not bound on the park like features, but understand that those who live in the area would like to enjoy this rare piece of public space as such and it is important to get it done that way eventually.
Also, it is important to have this trail paved so that it can be used in wet weather, and maintained for the winter (cleaning snow, etc. - like we like to clean our streets for car, we ought clean the trails and bike lanes for bikers and pedestrians - they are an integral part of our transportation network as well).
In closing, I am very excited about this project and can't wait to get my bike tires on this trail when it's done.