How do you feel about a wheeled dolly permanently under large floorstanding speakers?

I would use spikes if you have carpet and when you do want to move them, you can "walk them" by picking up three corners and pivoting around the fourth corner.   80 lbs is about what my speakers weigh and that works perfectly fine for me.   The thing is that the cabinets on full range speakers move a greater distance than the tweeter dome moves, so the sound is blurred significantly.   Putting them on wheels will only make things a lot worse.    If you don't have carpet, you can use a number of items to put under the spikes to protect a wood floor or use feet especially designed for sensitive flooring.   Do check out IsoAccoustics feet, the concept is sound and they are the only audio company of which I am aware that went to a NRTL to verify their claims - that is impressive in itself.  I'm using spikes on carpet which is over concrete embedded 6 inches in the earth , so I am not totally convinced those super feet would help my speakers.   Maybe?

Further thoughts ... Use spikes and when you need to roll them, "walk them" one corner at a time onto a mobile platform to roll.

You are making a simple problem into a complex one by thinking of a mobile platform. I strongly suggest you do not use a mobile platform, but simply put them on casters. I have used a few speaker systems on casters and they are wonderful for ease of positioning. 

People may insist that spikes are necessary to elicit the best performance. While that may be true, I have not found it to be the case. I have used many speakers that have spikes, and frankly, the speakers that have had casters performed better with casters, largely due to the elevation of the speaker raising the sound stage. In addition, there are literally dozens of potential advancements to systems, and almost never are all of them employed. Imo, spikes are among the least important of the changes that can be made to audio systems. While they can confer a change, it pales in comparison to what is done with power and signal paths. (I am not interested in arguing my advice with anyone here. If you disagree, great, do things your way.) 

A tangential point; most people randomly pick a position for a speaker system. With casters, you can experiment MUCH more with it, and most likely find a far better result. I would never put a big speaker on a separate, mobile stand, as it is far less stable, too. Talk about introducing unwanted vibrations! Casters would be far better in that regard. 

In real world system building you make the changes necessary to live with the system - or else you won't use the system as much, and or have trouble with the spouse.