One of my earlier employers exhaustively tried many of these strategies including generous referrals. Ultimately it came down to just a numbers game. Pay a reputable tech-recruiter for resumes, hit the grind, and you'll find some diamonds in the rough. If you have 30k budget to offer tempting bonuses, you should just hire a recruiter.
Tech hiring almost has to be approached like the NFL draft. Companies seem fixated on playing the free agency aspect, making lucrative offers to known entities and depending on word of mouth and reputation. Waiting on a 'sure thing' can cripple your business. They'd be better off interviewing and taking more chances on younger unproven commodities out of college without the rockstar resume and ego. A talented young engineer can become senior very quickly.