Adding additional inbound reachable nodes to the network does not solve any problems we have currently. This isn't bittorrent: we're not trying to get more 'seeder capacity' or the like.
Nodes without inbound connectivity still help the network out in terms of partition resistance (more than inbound reachable ones, to some extent, because their inaccessiblity makes some DOS attacks harder to target) and block forwarding and transaction forwarding (which improves privacy somewhat for others too), but the most important thing a node does for the network is what it does for itself: it independalty verfies the information that comes in and won't accept invalid data -- no matter what, and users running (and _using_ their own nodes) is the exclusive mechensim to that directly provides any incentive alignment for miners at all.
Under no condition should you say that a node without inbound is "leaching". It isn't. It means they're not contributing socket capacity, but the total node count has fallen so far that we're nowhere near that limit either. (And if we were a few people would spin up a couple more high capacity nodes on a few hosting facilities and neatly address that.
just sits there with a green tick regardless
It displays orange half-bars when there are <= 8 connections; IIRC the green tick is signifying that it thinks its vaguely in-sync with the network.
It does automatically use UPNP where available, though considering that so many of the resource usage complaints (which result in people not running the software at all) are related to inbound usage-- it might well be that furthering the misconception that one has to setup port forwarding to matter at all would just reduce the userbase further.
