I would like to see a discussion on the value of owning a publishing company if there is no label behind you equipped to track airplay.

Publishing and label ownership are two quite distinct concepts - and actually there are good arguments in favour of the two of them not being connected. I'd probably favour going after separate deals if I was a mid-career musician looking to exploit my catalogue... in an old school kinda way.

Tracking airplay and receiving the royalties you're owed is within the reach of any musician without a publishing deal, though it's not the simplest process. If you're based in the UK, you need to:

1. join PRS/MCPS - costs £100.
2. join PPL - free.
3. get PPL to assign you ISRC codes which need to embedded into all your tracks when you send them to radio. Audio editing software like Bias Peak can do this.
4. resgister your catalogue with CatCo.
5. once you start getting airplay, register the tracks with PRS/MCPS using they're online system, and they will start collecting your royalties.

What a publishing company can offer, that you may not be able to do yourself, is getting your songs to labels and artists looking for material, and also licensing your music to TV, films, ads, and compilations. In terms of sync licensing, though, it's worth approaching companies that specifically deal with just licensing deals. Search Google for sync agencies and pitch some stuff to them. There are other sync agencies that deal specifically with unsigned bands, but of these I would only really recommend Pump Audio - there are a lot of chancers in this field.

What Christian said

Also check out Ricall and YouLicence (YouLicence being a bit 'chancy')

Also, go direct to ad agencies if you think you have something they might like, and pitch your material straight at tv production companies - in the uk at least, a lot of tv productions are fairly low powered and they can be quite receptive.