Do you have any tips for attracting (or keeping) developers?
Yeah hire them. It helps if you are a programmer too and can talk shop with them. Presenting sexy tech helps a lot too. Helps also if you are likeable, reasonable, and demonstrate strong technical acumen. Mutual respect builds confidence.
Realize there are very few people who can possess all those skills, plus marketing skills, organizational skills, etc.. Not easy to find such a leader. Monero apparently had a core group of well-heeled guys (some that are also programmers) that gelled I believe via some connection to rpietila and David but perhaps I am mistaken. Probing my memory of the threads I read back in April, perhaps it was Tacotime that was the driving force.
Specifically for new coins that do not have much if any funding yet.
Nope. Get funding. Unless you are lucky to find well-heeled devs such as apparently Tacotime, fluffypony, smooth, etc.. But they don't want to corralled by someone into a project. They joined together because they had mutual respect and wanted to together address an anonymity weakness in the market.
Now that bitcoin has been relatively well established (compared to all other coins) it seems that most new development is going into supporting services and infrastructure instead of bitcoin itself. Do you see that as a pattern that will be repeated with other coins (that developers who come along after a coin has been established will be more interested in building supporting services instead of working on the core itself)?
That is the big question. Critical mass is well... critical. Blockstream's pegged side chains may help that a lot.
Monero appears to have its own community now and I am not following it, but for the brief moment I was reading their thread the other day, I saw others contributing a GUI. So maybe they are starting to get some traction on that. It is a big mountain to climb compared to Bitcoin's network effects.