I bought a basic serger about 15 years ago and it drove me crazy with tension and threading probs. Then I upgraded to the self-threading, self-adjusting tension Baby Lock (maybe 6 or 7 years ago?) and love it. Of course, when you want those 2 features, the machines get pretty pricey.
I have used it to make a quilt once (turned out okay but not my favorite). But I use it for so much more. Mine has a cover stitch and my daughter is severely vertically challenged so I use it to shorten sleeves on knit shirts for her and to shorten pant legs. Have used it to make pillows, pillowcases and slipcovers for home dec. Have been called on by friends & neighbors who can't sew to shorten prom dresses (the rolled hem does a great job on slinky fabric). I take it every year to the Cinderella's Closet to shorten dresses there and it makes a quick and easy spaghetti strap for the prom dresses(start with a long thread tail, put it inside the tube as you sew the long seam and use the tail to pull the whole thing right side out). Just used it at Christmas to make 8 denim aprons. I use it for all kinds of stuff and I can't imagine not having one. Like any other piece of equipment there's a learning curve but, once you get to know your machine, you'll be pleasantly surprised at what you can do with it.