The difference between cheap and expensive usually comes down to service life, brand name and coatings.
In general a new plug of the correct heat range and size will work fine regardless of whether it is platinum or not. The real test comes with miles. A regular steel or copper core plug will wear out after about 30K miles or so and needs to be replaced. A platinum should last about 100K although my experience on other brand cars is that they should be changed before say 80K.
On another performance site I have been on there was a lot of discussion about using platinum or regular plugs. For maximum performance, the concensus was to use regular plugs and change on a more frequent basis. For street driving platinums are fine.
BUT, BUT BUT. There have been some problems with leaving plugs in aluminum cylinder heads for the recommended 100K intervals. Many people on other sites have discovered that the incompatibilities(essentially corrosion) between aluminum and the steel of the plug threads, can lead to the plug being very difficult to remove at 100K miles. I hear many mechanics will not change Caddy Northstar plugs and send them to the dealer.
So some people recommend removing the plugs every 50K or so to clean and inspect and then put antisieze on the threads. If it was me, I would remove and replace at 50K, why put in old plugs if you went thru the trouble of getting them out? Plugs are cheap over the long run.
Good Luck,
Jim Henderson
