It really depends on the coin, from what I've seen, CAC can add anywhere from a 5% premium to a 100% premium (look at the selling price in MS Pre-33 gold for PCGS graded coins, CAC stickered gold coins sell for almost double in the same grade). I tend to think of CAC as a perk, a bonus, like credit card cash back... it's not going to get me to buy a coin I wouldn't otherwise, but when it's offered on a coin I like, it just makes the deal even better. In your example here, I would go with whichever coin has the better eye appeal to you. Which one do you like looking at more? Chances are other collectors will like looking at that one more too and will pay for that when the time comes to sell.

I agree go for the eye-appeal. The value of the CAC sticker is tied to the strike of the coin within the grade, not eye-appeal, so that is where the value lies in the CAC sticker for the investment value.

I believe it makes a coin easier to sell when the time comes. Sort of like an insurance policy.

I think the answer is always going to be "it depends" on these things, just like with Third-party grading itself. If you submit any modern coin and it gets a grade too low to be a desirable condition rarity then the value of the coin won't be increased and the grading won't pay off / pay for itself, but if you submit a coin and get a very high, conditionally rare grade, you win big.

If you submit a coin to CAC that doesn't have a major difference in price from one grade to the next grade up or down, getting the sticker or not isn't going to change the value much either - people are less sensitive to the 2nd option because going up or down a point matters a lot less. On the other hand, if you submit a coin where one point up or down can change the value by $500, $1000, or more, then getting the sticker could improve the confidence of the buyer in the grade and whether or not the coin is "good for the grade" and that could lead to higher value on resale.

At least, that's how I'd expect it to work. I've never owned a single coin with a CAC sticker and I've never submitted to them.

I would return the coin while you can if you feel any amount of regret at all.  And not buy the one with a mark on it either.  I don't know anything about Morgan dollars or US coins except that there are plenty of them.  I would set that coin type you want on a watch list on Heritage and wait for it to show up looking how you want it on a weekly US coin auction.  Unless this is such a rarity that it only appears in signature auctions... in which case you have a lot of money!  And watch Stacks, and Goldberg too.  No returns at auction, but, the photos are more reliable and the bidding usually leaves off below what a dealer will charge you to "buy it now." Of course check your change at Wendys also.  Till then, keep your dough for the opportunity to get one with no regrets.  Good luck