I'd expect that any engine that's had a valve regrind in the last thirty (>30) years would've had hardened exhaust seats installed (nice to have, but not so crucial on intake side).
If you are running an original, never updated head, I do not feel there are any additives sufficient to give back what removing the lead took away. The worst that can happen is that the valves will eventually recede into the head, the performance will suffer, and then you get a valve job done.
Depending on what your annual mileage is, that valve job may be a decade away; take Vette's & Healey Nut's advice, and have a ball!