Not sure what "DM skills" are. You mean like, carrying tanks, filling tanks, cleaning your boat, cleaning the shop, helping hand people their gear when they are getting in the boat, being a set of eyeballs in confined water training? There are no "skills" you learn in your DM class. Now if you want to take DM just so you can say you are a DM, then more power to ya, but do not fool yourself that you are picking up some cool new set of skills.
I don't think that's completely fair.
1) During my DM training, I spent a lot of time in the water being a set of eyeballs, but also working on hovering, in trim, and doing a lot of back kicking. And doing some of those things while task loaded with things like adding weight to a student, for example. Overall, I felt like my basic dive skills improved a noticeable amount during my DM training.
2) Other things you SHOULD learn during DM training include developing dive plans for a group and, more importantly, putting together an Emergency Action Plan to match your dive plans and group. Something that could be important for what the OP said.
3) Even if you have already taken Rescue, doing DM training ought to also result in some honing of what you learned in Rescue. Again, potentially valuable even if you're just taking groups of friend out to dive off your boat.
That said, if you get a DM card - so now you're a Pro - and you take people out on your boat, if you even accept $5 to go towards gas for the boat, you could be setting yourself up for a lawsuit if anyone ever gets hurt. Because you are a Pro and you have accepted payment, you could easily be interpreted to have a professional level of duty of care.
If you don't want to work as a DM, I suggest maybe borrowing the DM course book from someone and read it. Maybe just learn what you can from the book but do some other course if you want to hone your actual dive skills. I only know about SDI, but I can say for myself that if I had read the book and was considering doing DM but not planning to work as a DM, the book would have convinced me to skip doing the actual training.