Mounting Speakers On A Furniture Dolly For Mobility

Definitely not a good idea. Any good supports made for audio will sound better than those. 

You will probably get less bass higher up and more isolated from the floor which could be good or bad depending. Listen and see. No harm in trying and you will know how it sounds , nobody not actually there can know for sure. Just make sure it’s solid and stable and not at risk to fall and cause damage.

Also having large speakers on castors provides advantage to easily tweak placement for best sound which is always a plus.

If you listen to a pair of Wilsons on casters (before) and after when they are spiked, the difference is massive and it's not just due to a change in speaker height.

Having had my open baffle speakers on a pair for well over a year, they are excellent for finding best placement in the room, but once that's accomplished, the sooner they are off the dollys, the better. I my case, I didn't have any help, so smashed my big toe, sliding them off

Yes  use spikes as this will decouple to much and you will loose sound quality and bass detail.