I will try to keep this simple. For more depth find a physics text at a level suited to your current level of preparation.
Yes, the parts of an object spinning at constant speed are accelerating, but only toward the center. There is no energy being imparted in this acceleration.
If you are pedalling your bike at constant speed, you are not using any energy to accelerate anything significant beyond your own body parts.
Any mass added to your bike is additional mass that requires additional energy to accelerate in speed when you are in fact accelerating.
Rotating mass in the wheels and drivetrain is special when it comes to acceleration. Mass at the very center of rotation counts the same as mass that isn't rotating. Focussing now on the wheels, which are the easiest and most important to analyze, mass at the outer edge (i.e. the tire tread) counts 4x as much as the same mass that isn't rotating. Mass located between these extremes counts in-between, duh, 1X and 4X in accordance with its radial distance from the center. This weighting factor counts for acceleration only, not steady speed.
One final point, incremental mass such as spokes, etc., as rightly said above, does not really matter for steady speeds on the flat. It certainly does matter for climbing hills, as we all know. And, to be sure, all incremental mass adds to tire deflection, so in theory increases rolling resistance, but you'd be hard pressed to measure the difference due to a few spokes & nipples, given that the rim mass were held constant.