Got a thread discussing Jiang Wei, his life and exploits here. This is a slightly different thread, so I'm gonna leave it open for now, but if anyone else disagrees, this is the place to be.
In answer to your question, my feelings are that Jiang Wei should not have been the supreme commander of the Shu army. He was a very hasty man, to the point where he disregarded even the basics of preparing for warfare; his ninth campaign was started barely after the eighth one had ended. It is true that he had some minor successes in putting down rebellions and winning skirmishes, but overall, his campaigns cost the state dear in blood and treasure. This isn't necessarily his fault; it was too bad that reinforcements didn't turn up in one campaign, but that does not excuse his appalling conduct during the Chen Guan (right person?) affair where he let his supplies be burned by a defecting Wei general.
Jiang Wei acquitted himself well as a subordinate under Zhuge Liang, Jiang Wan and Fei Yi, but he was not a man who was fit for creating overall strategy. His loyalty can be commended and his last-ditch effort to restore Shu was an interesting and ingenious plan, but ultimately the weaknesses he created in Shu's defences and wasting of money and manpower far outweigh the meagre gains that he made.