In a word, YES, sell it and get the Purple.
IF you have to make a choice between the two, and as you mentioned you're doing mainly guitars, vocals, and bass.
However, if you have a bigger studio environment, and are doing drums, etc. the Distressor does have it's uses. Also interestingly, on a rock vocal, perhaps having compressed it a bit on the way in using the Purple, the Distressor can add some nice things during the mix stage.
The reason a lot of people say to use the Distressor on vocals during a mix, is that it's only at that point you can judge whether the types of harmonic distortion the Distressor adds are a benefit for your song.
Having experimented alot with the Distressor, I would never use it for tracking a vocal, because then you're stuck with what it 'does' to the sound. And it seems more often than not it detracts from the vocal.
Whereas with the Purple, it seems to sound great on just about anything, and you'd have to try hard to get it to sound bad. It also sounds great on bass. On guitars it's a toss up. If you have to comress guitars maybe you'd get more mileage out of the Distressor.