Conditional assignments with generics

Generally, Quartus isn't generating any unwanted logic. It's removing unneeded signals and registers unless explicitely told to keep it by synthesis attributes. The only disadvantage of using generics in conditional expresions is that you get some warnings regarding constant expressions. But it's the only plausible method to achieve conditional compilation inside a process, so the warnings should be accepted. You can expect a lot of similar meaningless warnings with parameterizable designs.