I have been collecting Marklin MAXI since the line first appeared. I guess I have about 20 or so locomotives, and not nearly enough cars, plus a lot of Marklin #1 gauge track. I'm considering selling most or all of the collection at some point, but have not really given it all that much thought yet. I do very much like the construction and running qualities of these #1 gauge trains--beautifully made in every respect. Nearly all of the stuff I have is still new in box because I've been living in apartments since I started collecting MAXI and simply have not had the space to operate my Large Scale trains. When I buy my next home, the outdoor railroad will likely be LGB because I also have a fairly extensive collection of LGB trains.
I don't know of any club specific to Marklin MAXI, but there are a few Marklin enthusiasts groups on Yahoo and elsewhere. You might try Googling "Marklin MAXI" and see what comes up.
Get the Garden Railways newsletter delivered to your inbox twice a month