I would keep both. The Magnifax is a great enlarger. Working with two enlargers is not a problem IMHO even at the learner stage; on the contrary, it keeps your mind free from overconcentration on a single piece of gear. Enlargers are much simpler tools than camera lenses; concentrating on the intricacies of a single one isn't really worth it IMHO because there aren't any.
Get a good lens. For medium format this is not as critical because enlargement ratios are less, but doing some hunting for a cheap Rodagon, Meogon or EL-Nikkor is probably worth it. Enlarger lenses are cheap.
The Color 3 head is not stabilised (or rather its transformer isn't). In theory, if you have a problem with changing voltage in your mains lead you might want to get a stabilised transformer eventually; because the bulb runs on 12V, any transformer for halogen lighting will do. (In theory the enlarger can run off a car battery.) However I have the original unstabilised transformer and no problems with it. If you are into soldering: the transformers are usually set to 220V, meaning reduced bulb life as most European networks are now on 230 to 240V. The transformer actually has a 240V setting inside; you can just solder the wire off the 220V end and on the 240V end to conserve the bulb and/or the fuse a little bit. I did that when the fuse burned out on me during the first hour of darkroom work
For the Magnifax, one accessory that is really
worth it is the fine focusing gear. It's available from places like Fotoimpex (called "Feinfokussierung"). It allows for much preciser focusing. There is also a flexible attachment to the fine focusing gear that allows you to focus more comfortably without having to turn gears over your head; also worth it IMHO. Also remember that if you use 6x9, for the colour head you need the 6x9 styrofoam mixing box - easy to recognise, as the others (6x6 and 35mm) are all square, and the 6x9 is rectangular. In theory you can use the appropriate mixing box for every format to get slightly more light out of the enlarger, but I find changing the boxes every time to be more hassle than it's worth, so I end up using the 6x6 box most of the time (I hardly print 6x9).
The main problem with the Magnifax is that because it's possible to tilt the head sideways, the head and baseboard might not be parallel when you set it up. There are a number of techniques for aligning the enlarger head; one of the easiest uses two mirrors, one facing up on the baseboard, the other facing down in the negative carrier. For the upper one you can either use one which is about 6x9, drill a hole in the exact center of the reflective coating so that the light goes through, switch on the enlarger and see where the dots appear in your darkroom. This is a hassle because of the exact center. Or you can use one which is wider, so that it sticks out in front of the enlarger head, scratch a small hole anywhere in the extended section, look through that down on the mirror on the baseboard and see where the reflections from the hole appear and where the reflections from the negative carrier are tilted. It sounds more complicated than it is. Or you can just use a spirit level if you have a precise one. There are specialised setups for this with a laser pointer, but it's probably not worth it. If you have access to a laser unit such as the one used by carpenters and construction workers it might be worth borrowing it for half an hour.
For colour filter settings, I would dedicate an evening to find out what colour filter settings produce what gradation on your paper. You get two things out of that: firstly you can have a handy table with colour filter settings, secondly you get to know your enlarger really well. You can do this by trial and error - take a normal negative, print it at various settings and see what happens. You can also go for a more systematic approach, such as the one outlined by Ralph Lambrecht in his paper "Contrast Control with Colour Enlargers
" (PDF - this is a chapter from the excellent book "Way beyond Monochrome
"). It's a bit of an intimidating read, but at the end you know everything about your paper and your enlarger, and it's worth it in my opinion.
The main advantage of the systematic method à la Lambrecht is that you get filter values that keep your exposure time constant. With trial and error, usually you have a table like "gradation 2: 30 Y, gradation 3: 10 M, gradation 4: 60 M". Because the filters darken the light a little bit, you end up with different exposure times for all the gradations. With a systematic table, you get "gradation 2: 60Y, 15M; gradation 4: 10Y, 70M", so the light has the same effective brightness, and you can just choose a different gradation without bothering about exposure times. This alone is a huge bonus in efficiency for your darkroom work.