As a live aboard or cruiser, I cannot imagine not having an arch or davits. It is true for long passages, you throw the dink up on the foredeck, but truth be told, I crossed the gulf with her up on the davits. We were in some pretty nasty stuff and it did fine. In fact, with one exception, I have never had a concern about her being swamped. It is a risk though and if I did not know my weather for a few days out, I would put her up on the deck.
THe trick as you can see above is to tightly secure her to the stern of the boat so whe will not swing. THe best thing for this is ratchting straps (as seen above). However, I also use a combination of lines when I don't feel like fishing out the straps. You will be lucky to get more than a season or two out of a set of ratchets as they will rust.
Here is a pic of our system:
As you can see, we have both davits and an arch. THe arch was custom made. I personally prefer aluminum to SS because you can get a lot larger diameter tubing without the weight. THis is important if you are going to be adding panels or other things above the arch where multiple wire runs take up space. I think the arch above weights maybe 80 lbs. I can easily lift it by myself. Some of the equivalent Stainless Steel options were incredibly heavy and incredibly expensive. THat is why we decided against stainless. I have enough weight in the stern already and didn't need to add hundreds of pounds more.
Why do you have to have an arch or davits as a live aboard/cruiser? I can see a lot of reasons.
FIrst, your tender is your car and gets a LOT of use. I find hauling it on/off the foredeck to be a real pain in the butt and it is unsightly to me. ALso, it will likely cover up hatches that block ventillation. As such, you will probably only find her on the deck when making a long crossing.
Leaving your tender in the water for long periods of time (depends on your location) will cause a lot of barnacle and crap buildup on it. FOr some, there is also the security issue, but that has never been our concern. After about three days straight of being in the water, she gets a nasty film and in some places, small barnacles. THat becomes a major issue (esp for us).
ANother reason to get the dink out of the water is that most of your jumps are local. Pulling the tender behind you drops about one knot off your speed. If you can easily get her up, you will find better range and better time to anchorages.
Regarding arches versus davits:
Like Rick (Vasco) said, I would opt for the arch over the davits. I have both because a the time we were gong to just use davits, then changed our mind as we opted to start adding panels which our davits would not accomodate. Your arch can most certainly be designed to lift your tender too. And with an arch, you do have the option of panels, wind, storing fishing gear, adding lights for the stern, etc that are not as easily accomodated (if at all) with davits depending on your boat design.
THe cost of the arch is a lot more but was worth it to us. It may not be to you. I personally would not be without davits or an arch as a LA/Cruiser, though some make do without. It has certainly made our life more enjoyable.
THese are my opinions. Hope they help.