i think this is a bad idea in general because people who have alot of gems and gold will be able to make themselves unstobbale and even with limits on it it will make them very strong. As for the chakra part people who stay at lvl 15 forever and just keep increasing their chakra will be able to use these as many times as they want
1. You're already unstoppable with some of the current Jutsus o.O This is mostly for fun and another thing to use gems on instead of HP and mounts. Anyway, you won't be able to make yourself a "god" character with this untill you hit around the 100 DK mark, and even then it wouldn't be that easy... And at whch point you would already be a "god" character because of Kyuubi and those "some" jutsus
2. Let them stay at 15, they'll be missing out on the other upgrades they could be getting at a higher level ^.^ And (saying Neji does alow that pvp part >> << >>) You need need the high DKs in order to get it... Not to mention the 1k gems alone...
3. I don't like people with alot of money because they could buy themselves a kyuubi to level themselves at Genin =( The way I see it, if you have the gems and are willing to spend the hundreds it would take to make yourself "Unstoppable" for a few fights a day then sure, why not? You'll have to spend another couple hundred to find the perfect combo of moves but it shouldn't be that easy because of all the choices.