Not and engineer here, but do know some basic stuff about computers.
2007 is really old in terms of computing, especially if you do stuff like music production (for just typing word documents it's fine for example). Upgrading your RAM will help to some (probably small) extend, but you'll still be crippled by the old processor. Since the 15 inch rMBP has PCIe based flash storage as well, the overals experience of upgrading will be significant. (although, that storage is expensive so you'll need some external storage probably).
I don't want you te spend money if you don't have to, but if you can afford it and current gen MBP would be a major upgrade IMO.