I have 2 Shop-Vacs (one that's 4 gal 5hp and another that's 12 gal 5.5hp IIRC), a steamer, and I also own a LGCM (non-heat) model. For a weekend warrior, IMO I don't think you'll regret the purchase of an LGCM considering its price. For me, it's not a purchase that I've regretted. I've used it on the cars and around the house. Heck, if I had to pick, my Makita was a bigger impulse buy as that sees nowhere near the amount of action I would like, especially considering how much I paid for that machine.
Some people will say that you can do the same thing with a good shop vac, but here is my opinion on it. I've tried both the shop vac and the LGCM for interiors, and if I had to pick the winner between the two, even though the shop vac is more powerful I find the LGCM to do a better job. What makes it better is the attachment itself.
First of all, it has a very small opening so despite the machine being less powerful, its suction is just as good if not better since the power is more "concentrated" through the smaller opening. I apologize if I'm using the wrong terms, I just can't think of the right words to explain it at the moment.
Also, because the attachment is clear, and the unit itself is clear, you can see whether or not you're pulling up clean or dirty water. This gives you a good idea of when the area is "clean enough". I say "clean enough" because obviously the LGCM cannot replace a hot water extractor and you can sit there all day doing pass after pass after pass and still pull up dirty water.
The 12 gal Rigid "Xmas Special" shop-vac I got is a BEAST when it comes to suction power. I have not tried this as a wet-vac in the car but based on its performance so far, it might be a little better (if not a lot) if using it to extract water. Again though, the attachment is not clear so I still give that advantage to the LGCM. Plus, the LGCM sprays clean water and extracts at the same time.
As far as the steamer, I've been enjoying its uses in the interior. It's a bit less effective on carpet/upholstery so it's probably not a replacement for an actual hot water extractor but it does a pretty decent job considering the time and effort involved, not to mention how dry or how quickly the fibers dry.