I completely agree that self up voting is ok if you post something which is really good content.

While self voting has its uses, I was thinking more along the lines of upvoting people you know will get you curation rewards with regards to balance. Curation also goes straight into SP which is of benefit to those you're voting for.

Self voting I reserve for competition posts where I want to try and increase the reward pool, not that my vote is worth much. I also think if you're going to do it, then do it after the majority has upvoted so you give them the better curation reward benefit.

The trouble is new members are like hot potatoes. Not many people want to touch their content no matter how good it is.

Sad, but true. At least for those who could actually make a difference. It's also getting harder to find good content in amongst the flood of daily posts. There's no reward for it to encourage it.
I recently reported an account to steem cleaners which had a bot posting copy/paste every 5 minutes. It wouldn't take many of them to clog up the new feed.

When I first started I could see the higher ranking members got more rewards, so naturally I thought if I up voted their content I liked I would earn curation rewards.

It took me a while to even discover I could get curation rewards! 😆