Note: I read the first page and kind of skipped a bit on the second, so what I'm about to say might have been said before. If so, sorry :3
Also, it's pretty late for me right now, so this turned out to be a pretty confusing post. Have fun!
----
I was there when township Herogates were in effect and I was PVPing quite heavily at the time. In fact, it was pretty much all I did on MC. What we saw back then was that everyone just used their towns' Herogate instead of walking where they had to go. Finding a player in the wilderness was extremely rare.
More instant travel will only lead to shorter ways, less travel as a result and less PVPers that care enough to prey on the lower amount of moving players. Furthermore, they encourage camping (bigger groups).
Gates in any form actually do the exact opposite of what you're trying to achieve. They don't open up the map but reduce the active parts of a map to the routes between gates and towns. There won't be more PVP, it will just be elsewhere and it will only lead to PVP parties focusing on those active parts which in turn leads to massive clusterfucks that are entertaining but not what you seem to be looking for.
Basically, if PVP parties are too much to take on for you, you are too late to the party or you don't want to kill noobs, then I'm afraid the reasons for you finding nobody to PVP lie solely in your own person and can easily be fixed by being in a PVP party, being in said party ON TIME or killing the noobs respectively.
Advantages 2, 3 and 4 OP stated are not worthy of discussion and I already stated my opinion on 1 and 5 above.
On the subject of PVP arenas:
The thing here is I think that everyone needs to decide whether they want open world PVP or skirmish-style PVP since many players seem to like both and both also have their advantages over the other.
Personally, I think that the current ranking system is unnecessary and that it discourages conventional Minecraft PVP. Furthermore, arena type matches make it pretty much impossible to sneak up on an enemy as everyone expects to be attacked anyhow. I agree with the notion of entirely taking out these instant-action systems for PVP.
My reasoning is that if everyone currently fighting in arenas was forced to find enemies in open-world scenarios, there'd be more open-world PVP overall, right?
TL;DR: If you want solo PVP, delete all forms of instant travel and instant arena action.
You probably still won't have a lot of it, but the chances of encountering a single foe will be higher with all arena and skirmish prOs out in the wild.
Heroes still sucks!