Problem is, it's sort of PD's fault as well as our own. Let me explain why you should and why you shouldn't, and perhaps the choice will be clearer to you:
The credit payouts are way too low. As some have stated here on this forum, it would take an insane number of man hours to reach 20 million, let alone the 50 million credit cap. Why there's a credit cap is beyond me, still, but it's there so I guess we have to live with it.
The problem with the whole thing is credit payout vs. car count. There's just too much cars to enjoy to not do the glitch, as I myself would've never been able to fully enjoy all the content this game offers considering I've got a time schedule beyond playing GT6. It would be a shame, because it's so crammed full of good stuff that otherwise I would've never seen.
This is a complement to GT6 as a whole. The game is good, nay, the game is great. I want to see it. I want to see it all. Yet I can't, the ordinary way, because I don't have the time.
Older GT's remedied this in a plethora of ways. First, you earned gift cars by the buckload. Second, those gift cars weren't one time only prices. They were given each time you completed a championship. Third, the gift car per championship could vary between two, or three or perhaps even four different cars for a single championship. Thus also giving the player a reason to complete championships multiple times, thereby stretching the worth of the single-player mode significantly, because you WANTED to know what the other cars were, and many times there wasn't another way to obtain said cars. There was an incentive to play these championships over and over again, not only for the gift cars, but the amount of money some of them could be sold for.
It basically gave the single-player almost infinite amounts of replay value because there was so much left to discover.
Right now, all cars (or almost all) are buyable from the get go, provided you have the money. Problem is, how much time are you willing, and more importantly, how much time ARE YOU ABLE to pour into the singleplayer. When I was playing GT1 or 2, I was in elementary school, so yes, I did have plenty of time. Right now, I'm 24 years old with a girlfriend, other friends, I work in the weekends and go to school five days a week to study to become a history teacher, ultimately a very satisfying but quite a time-consuming study. I still have some time over for playing GT6, but nearly not as much as I used to. So that is where your decision on wether or not you should use the glitch should come from. For me, it is almost a necessity to do so in order to ENJOY THE GAME. Is that bad?
Well, it shouldn't be, but it is. It feels bad to do the glitch, but it feels even worse that I need to do it to get some enjoyment out of playing the game. I don't think it gives me an unfair advantage either. You see, I know I'm not the best of drivers. I'm pretty good, and I can handle some of the more difficult cars on the Nurb (like the F40 and Yellowbird), but I'm nowhere near some people on this site.
Will a credit boost give me an edge? Nope, because there are still people on this site that have me and my FXX eating dust while they pull away from me in a souped up, completely tuned and utterly well made Civic. It doesn't make me drive any better at all, especially now that I'm getting used to a new G25 with clutch. I've never driven a car in real life before, so I've got my hands full with learning how to drive stick. So no, it won't help me one bit.
Does it give me the satisfaction that I used to get from older GT's? No, not at all. Working for the money always feels better. Yet people should be able to work for it. Right now, it's an impossible task to do so because of the lack of features stated above, features that not only made the grind less time-consuming, but in my eyes made GT better as a whole.
I want to drive different kinds of cars. I want to upgrade that Viper to an insane 1300HP rally monster and try to make it competitive. I want to see what I can get out of that small Opel Corsa. I want to try that Peugeot LeMans car everyone keeps talking about. I want to try all the different rally cars and I want to build my own. I want to put in records on the Nurburgring and see with which car I can be the fastest. I want to try that XJ13 and see if I can handle it. I want to see the difference between a Lamborghini Diablo GT and GT2. That's my enjoyment for the game. Without the glitch, that would not have been possible, for me at least.
However, it is possible that PD will change the prize cars, as well as money payouts. GT6 isn't done by far, as is stated by themselves. Car prices have for the most part already been drastically reduced. If they do it well enough, I might delete my save-file and start all over again. I would have no problem with that. I like the grind, but only up to a certain level.
What kind of person are you? Do you have the time? What is your enjoyment, and how do you get it? It's your game, and you decide. You might have worked hard for that Nissan GTR, and I might have not. When we meet online, will I be the better driver, will I have an unfair advantage when we go head-to-head? If you are the better driver, no money glitch will change that fact. You will still be faster in the same car.
I hope I made something more clear for you, and I hope I helped out other people here as well with this moral issue. Decide for yourself. Decide what the game is for you, as I've decided what it is for me.
