Well, since this is already restored, I think the restore vs. leave it alone side of the discussion is moot. It just doesn't matter. The restoration has already been done, and it's just a determination of whether you want a restored one, new one, or original.
My opinion is that they are all going to be about the same price, give or take $100. The TCA used to make a blanket statement that a restored piece should not be valued any higher than it's original counterpart in VG or C-6 condition. They have since adopted "restored" grading standards, but make no mention of monetary value for each grade, as that is between buyer and seller.
That being said, it seems that the general rule for restored pieces, that they are worth maybe half to two thirds of an original in excellent condition, which is about the value of a C-6 piece. There are some exceptions, I am sure, but I'd say that's pretty much the going philosophy. Most collectors of original equipment would only consider restorations (or reproductions) only when the cost of a good original is extremely high, or the piece is so rare that it becomes a challenge to find one in any condition.
As for this blue comet, the train is sufficiently common that you could probably find an original in decent condition for relatively the same money. However, if you ever performed a restoration, you would understand why the person doing the work is asking that kind of money. It takes a lot to do it correctly.
Which is another point you have to consider. Is the set done correctly? Does it look like the original? Are there parts painted that shouldn't be, like drawbar pins, etc? Are the colors correct with respect to the originals? All this needs factored in. If the blues are not correct, then it's obviously not worth what a properly painted one is worth, etc.
Also, when considering a restoration, do not find yourself paying more for a train painted in a hard to find color. There are a lot of restorations of 636 City of Denvers done in Girard green, and advertised as "rare". While the originals are extremely rare, it makes no difference when restoring whether you use green paints or yellow and brown. It becomes a personal taste issue, not a collectibility or rareness issue.
At the price point you are looking at, you also have the MTH reproductions. Nice finish, etc, new, warranty. If you like the "new car" look, then maybe these are for you. They won't hold the value of even a C-6 original, but then again, a restoration probably won't be much better. I would have to say that a properly serviced older train, in any cosmetic condition would probably be easier to use, work on, and be more reliable than than the newer reproductions. Read some of the reviews in this forum on modern tinplate and make a decision.
Just examine your needs and wants and go from there. It's personal, ask for insight, but you'll be most happy if the decision you make is made by you and is not made by the consensus of or majority opinion of forum members.