Hardware

Not really in most cases. The decoder might need to spend some more transistors to accommodate the instructions but that should not be much. And the very oldest never used ones can be thrown to some very slow microcode rom or something. In the execution side SSE uses the same registers as the latest AVX does. And the low level compute operations actually done by the execution units are the same. You need to understand that each instruction is actually translated to one or more micro operation by the decoder, they are not direct execution control data.

However there are some old no longer used features in x86 CPUs that do complicate the design somewhat. And there are instructions connected to those features. But that's really not the instructions themselves using the die area. Intel's x86s standard proposes to remove for example the middle privilege level rings and call gates from the CPUs. As well as some no longer relevant memory access modes.