So, since v.29.0 has dropped UPnP support (as i now understand it) my BTC Core application was unable to accept incming connections any more. But that is the most important feature for me, as i consider supporting the great BTC network as an exclusively important goal.
While accepting incoming connections is definitely more helpful, not accepting incoming connections still supports the Bitcoin network. You still be receive and validate all blocks and transactions, and forward the valid ones to your other peers. The terms "incoming" and "outbound" only really refer to which node initiated connection, they are other approximately identical as data goes in both directions.