What reopening Simon's Town would require

Does the Royal Navy still use Simon's Town, and would reopening it as a fuller base be worthwhile?

Only if Britain can fund the ships, personnel, and recurring activity that make a forward base worth maintaining.

A naval facility does not by itself create useful presence at Simon's Town. A reopened or more active base needs ships assigned to it often enough to justify maintenance, administration, and recurring activity. It also requires crews, recruiting, support personnel, and the budget to sustain the whole organisation around the pier. The real decision is whether the Navy can generate and use a forward-based force, rather than whether an old site can simply be declared open again.