This is a topic that will be debated until March...and then 6 months after that, and...
If and that's questionable at this point, Apple does go to a twice yearly update, we have no solid proof that the Mini will be updated in March or if it will be updated in the Fall. And no one can be positive that retina will come to the Mini at either time.
The Mini is a good product now, the 4th gen is a good product now, if you want to wait until they are a better product, then that's what you should do. But keep in mind that 6 months after you purchase..another upgrade is just around the corner.
For myself, I'll enjoy what I have right now and will still enjoy it when upgrades come around, I will decide then to sell and buy the latest and greatest or wait until the next go around.
Good luck to you in March! Hope things work out the way you want!