My VHF is vintage 1982... like a rainbow in the dark, YEAAAAHHH.
After trying to hail the tow/barge/dredge thing and getting no response, I think it's possible my antenna or radio is crap. We did a radio check, but at like 200 yards. We monitored 16 and heard nothing for 5 hours.
Having heard your input, I think I'll seriously consider a new main unit with auxiliary handset. Nav wise, I want to go the tablet route but also like your idea of a GPS distress/man overboard function. Do you need one to have the other?
A couple of notes.
1. Radios don't tend to wear out. Yes, a new radio will have a bunch of great features like DSC. But my guess is that what is more likely the problem is that you masthead antenna and the cable running up to it are shot. They don't usually last 30+ years. On VHF the ground is usually less of a problem but you should check the ground wire too. And to answer your question directly yes you need a GPS attached to the radio for full DSC funtion. It will still work without one but will not broadcast your position if you get in trouble.
2. I do a lot of offshore long distance sailing. If I have learned one lesson it is redundancy, redundancy, redundancy. A fixed mount VHF with a second mike is very convenient. It it craps out you have nothing. A fixed mount VHF with a second handheld radio means two things have to crap out before you lose comms. About the same cost. (BTW I have two fixed mount and two handheld marine VHF radios on board. But I am a belt and suspenders guy.
Of course, three "good friends" of mine have years of experience and were "happy to go out with me" any time. A 63 degree sunny afternoon and three friend's voicemail boxes later and I decided it was go-time.
3.I am glad you had a successful sail. But I would caution you that you made the mistake of many new (and less new) sailors. You decided to sail under less than optimal (appropriate) conditions as your friends could not come when you wanted to go sailing. I have watched people sail into 45 knot winds and 20 foot seas because they needed to get to the next port on time to meet friends. They did. Lost the dinghy, most of the rig, and a big part of the transom. I guess they didn't take their friends sailing. There is an old saying, originally attributed to pilots but paraphrased: There are old sailors, there are bold sailors, there are no old bold sailors. Don't let desire overcome common sense.
Fair winds and following seas