Whenever an intro comes in, I divide it into one of a few buckets and immediately send a mostly rote email back quickly:
* Highly interested - schedule a F2F or phone meeting within in the next week, suggest two dates to discuss more ("Wow, that sounds cool, would love to catch up in person to discuss more, are you available X or Y? I'm based in A but willing to travel anywhere around B")
* Kinda interested, being polite - suggest a phone meeting and strongly time box it ("This sounds potentially interesting. I can do a 15 minute call at X before my next appointment)
* Non-commital - Ask for more info, put the onus on the other party. ("Hey, would love to hear more about this, can you forward me X & Y so I can get a better understanding of how I can be helpful?")
* Useless - Polite brushoff ("Hey, I took a look and I don't think I'm the right person to help you with this for X & Y reason. Maybe you could try A & B? Thanks")
I think the key was to not put so much onus on the next step. By the end of the intro, I barely have any info, my main goal is to gather more to make a decision.