I must say I never liked steel cables, but that is personal really, non scientific.
I modified the wheels to take strings and later changed the wheels for some designed for strings. If you are able to make strings, there is no real problem. Having to get them made is a bit of a fuss.
The limbs have been upgraded too from TM2 to TM4, no problems there;Merlin made sure the fittings at the shoe ends matched the old riser.
Changing cams can be much more difficult to get right as so much depends on the profiles on the cams and the stiffness of the limbs that match with the poundage you want.
Much depends on what you want to do. If you upgrade the limbs, cams and riser; you end up with a new bow!
I suspect that the older round wheel bows, being slower,would not perform so well in the wind as some faster models. Indoors; I can't see that they would be at a disadvantage. I believe Robert Ragsdale thinks along those lines.