I just picked up a Cold Delta Elite a couple of weeks ago.

It is factory original.  In fact, it doesn't looks like it has ever been fired or field stripped.

I would like to replace the original (plastic) guide rod and recoil spring with better technology.

A heavy enough spring for full power loads.

There are SO many aftermarket parts for Colts that I don't know what I'm looking for.

It looks like Wilson is accepted as being about the best there is.

I hate to be so utterly helpless, but can someone give me a source/part number for what
I should get?  

This is the polished stainless version if that makes any difference.

Also, I read that a stronger magazine spring will help in reliability.  Is that true?

I have a Kings setup for my Delta Gold Cup.  I comes with a King full-lenght guide, stronger recoil springs, 2 rubberloid shock-buffs, and a recoil spring capper.

As for guide rods, use a steel one.  What kind isn't a big deal as long as it's high quality.  USGI is fine, so is any FLGR you want to use.  The plastic one will break.

For springs, I'd say 22lbs would be a good place to start.  The Colt two-spring set-up is actually OVER sprung, at the wrong time.  Too much spring will slam the slide forward too harshly and cause battering problems too, so don't start thinking that you need a whole lot of spring.  You really don't.  Start at 22lbs and go from there.

Replace your firing pin stop with an EGW flat base FPS.  What that does is increase the amount of force required for the slide to go back.  It does it through using a different geometry against the hammer, so cocking the hammer takes more umph than stock.  So more power of the slide going back is absorbed in the system, without really doing anything to your springs or otherwise dicking up your gun.  It's all about leverage and geometry.  

Shock-buffs can't hurt.

Set-up properly and a DE will last as long as any 10mm.