Modern cars:
Rust proofing is much improved.
Seats are, generally, more comfortable.
Engines don't need de-coking every 30,000 miles (may be more to do with petrol quality).
Brakes, handling and steering are MUCH better (if sometimes lacking in feel).
A LOT safer.
Engines produce far more bhp/litre in standard trim.
Old cars:
MUCH easier to maintain and repair.
A lot lighter, so tuning has a greater effect.
Different.
Car clubs are very friendly with far less upmanship and far fewer boy racers.
Although underpowered, they seem fast due to marginal steering and handling on narrow tyres
So more fun at slower speeds.
Owners of old cars tend to me more [FONT="]knowledgeable[/FONT] (IMHO).
Less likely to be able to drive car faster than your skill level.