Besides cost and perhaps overall amount of allowable spring travel, what other tradeoffs are involved between a spacers vs. a spring/coil lift? (in my case an overall lift of 2.5" to 3" is all I need)

 

you will experience a rougher ride with spacers vs coils and shocks.

 

Aside from being economical, the only benefit spacers provide is lift for bigger tires, looks, etc, but they change the suspension and steering geometry just like springs, they have all of the same drawbacks.

Spacer lifts are very popular just look in the Show and Tell Section.