Mags on the whole are very, very reliable. And, sorry to explode the myth but the Bendix single drive, dual mag is just as reliable as any 'normal' mag. Okay, there is potential for a big problem if the single drive fails but can anyone quote an example of this actually happening?
500hr inspection is just that - an inspection. It may show up worn points, cam or other parts. What it doesn't do is tell you how long the ignition coil is going to last. Much the same for an overhaul. Don't be fooled into thinking it's a guarantee of 500 hours trouble free future use...
Impulse coupling springs do go weak and are often the cause of intermittent starting problems - impulse disengages at cranking speed but 'clicks' when turning the engine over by hand, just to put you off the scent. Gipsy Major mag tapping is to free stuck impulse couplings.
For some reason total mag failure seems to occur more often on the ground between flights rather than when airborne.
Bendix mag inspection is 4 years calendar time - inspection preiods aren't just by the hour.
Fouled spark plugs can be avoided by correct shut down procedures. Lycoming's advice is to run the engine at around 1700rpm (if it's clear behind) for 15-20 seconds then back to 1200rpm and mixture straight to idle cut off. The lead scavenging agents in 100LL work better at higher combustion chamber temperatures which is why the higher rpm run down and leaning whilst on the ground helps keep the plugs clean.
It isn't just the lower plugs that can get fouled. With an excessive mag drop during power checks, aggressive leaning may well clear the offending plug. Try it three times and if it doesn't work, don't fly - seek help. I heard of one aircraft owner who went flying round the circuit to try and clear the plug after leaning it didn't work. That didn't work either. So he flew one plug down to his maintenance facility some 30 miles away. Not a very good idea...
Despite the good things about mags, the future is ignition systems like the Rotax 912. In fact the Rotax 912 is the engine of future GA. Be it in Rod's MCR01, my RV-12 or an IFR certified Tecnam P2006T twin.
PS No vacuum pump likes being turned backwards (same ones are fitted to Continentals as Lycomings). The carbon vanes are set to sweep (angled backwards) in the chamber and they can break and jam if turned the wrong way, causing the pump drive shaft to fracture (as it is designed to do to prevent potential engine damage).