OK so I've got to replace my tires.

My Continental Touring Plus on the rear has developed a bulge.
Though I've been fairly pleased with this tire overall, I wanted to replace it with a Marathon Plus.

LBS stocks normal Marathon in 700x28, 32, and 35. I could have them today and be riding them tomorrow.
The Marathon Plus I'd have to order, and figure out some other way to get my bike up and running in the meantime.

My route is cactus/thorny-plant -lined bike path, then through an industrial area to the airport. Normal tires don't last very long between cactus spines, thorns, nails, staples, and broken glass.

Do I sacrifice a great deal of puncture resistance if I go with the Marathons vs the Marathon Plus?

Any advice is welcomed

YES.

You'd be missing the whole SmartGuard thing that Schwalbe has in their Marathon Pluses. On their website the Marathon Pluses are in the 'flatless' category. (Remember, flatless, not flat-free)

Personally, the only tires I will run other than the Marathon Pluses, are Nokian Mount and Ground in the winter.

"Plus" you can also get them with reflective sidewalls. I love mine, but have ridden no other tire in a similar category. Due to the flat protection they are quite thick and I had some height clearance issues with 28's on my older schwinn road bike, width was totally fine. 25's fit nicely and ride more like 28's.

Where is Kojac when you need him?

There is a poster here that could answer your questions. He goes by Kojac.

I can't think of anything to add to this post. If you're in "Thornville" USA, the plus is the way to go. The standard Marathon tires do have a really effective kevlar belt, but the pluses are definitely a step above in terms of flat protection.

And for the record, our entire Marathon line of tires come with the reflective ("reflex") sidewall. In fact, it's the only way they come.

Kojak, thanks for your input. I recently purchased my first set of Marathons (700Cx25 by the way, not Plus), and am enjoying the security of having low probability of flats. One thing I noticed about these tires, that I haven't experienced on any others, is that they drift very noticably when cornering. It was very disconcerting at first; now that I am used to it I just take corners more cautiously. I think the drift is an artifact of the relatively aggressive tread on the shoulders of the tire, and perhaps a characteristic of the casing construction (though I think this is less important).
So, if my input as a potential future customer is worth anything, I would like to see a similar Schwalbe tire that did not have this drifting characteristic when cornering.

Hmm, my 700x32 Marathons (with 3000 miles on them) feel just fine going through a hairpin turn at 30mph on my commute.
(https://maps.google.com/maps?q=la+jol...09602&t=h&z=17)