If a startup sells into IT departments, is it beneficial for that startup to enter into a relationship with IT research and advisory firms like Forrester, Gartner, etc.?
Do these firms bring exposure and credibility to a startup? Or would the time and money invested in such a relationship produce a better return elsewhere?
From my experience with these firms, most of them are basically hired guns, you pay them a lot of money to get visibility.
Which may not be a bad thing. If you're a VC-funded, cash-spilling-out-of-pockets-off-your-aerons startup, then yeah, Garnter and friends may be a good deal - just a like a high priced marketing firm, or an entrenched channel reseller would be - a way to get your clients attention.
On the other hand, for most other startups where money is actually important, I'm sure you have better things to do with your money - like creating value, spending time with the few clients you have, etc.
Just don't expect them to be giving you free publicity.
Difficult to answer, but I'll try.
I actually had a very good experience with a (small) industry analyst firm. Besides good conversation with them, they helped us doing a video-podcast interview and mentioning our company in quite a few opportunities. I remember, in a specific period, Google Analytics showing us a lot of visitors in our website were coming from the analyst blog.
That said, it's very difficult to estimate a ROI for these kind of investments.
If you already have customers, get in contact with them and ask them directly. How do they learn about potential new products? Do they read sector magazines? Do they go to conferences? Do they rely on suggestions coming from developers?
That should help you to understand how to connect with other potential customers.