I answer this question alot -- I need to put a response in a word document on my desktop so I can copy/paste it
When reforging, the first thing I do is optimize for haste and get haste wherever I can. After that, I take remaining gear that I haven't reforged and optimize it to get over the hit cap but by the least amount possible. I may do some reforges to spi/hit to crit here or vice versa, whatever gets me over with as little wasted itemization as possible.
After all that is done, if I have any gear remaining that a) I haven't reforged and b) has Spirit on it, I reforge that Spirit to Hit. This is a 1 for 1 trade as both stats provide hit rating with Balance of Power. However, while we get absolutely zero value out of Spirit regen during a boss encounter, our Treants do get some value out of the Hit. So Hit is marginally better than Spirit for us. This is not groundbreaking or insanely significant. I parsed my logs and Treant misses when I had 0% Hit (all hit obtained from Spirit) were less than a 20 dps swing. But, on the gear where I reforge Spi -> Hit, there is no better alternative so it's just a min/max decision to make that reforge.
Long and short, it helps a small amount and, I no longer have a serious resto offspec where my gear needs to pull double-duty (for Resto, the Spirit would be significant regen). The only resto I do anymore is healing the heroic daily for some valor points on occasion -- honestly the hit helps on cc and I don't need the extra regen for heroics imho. Anyway, if you do any serious Resto offspec, I'd avoid these reforges. If you never do anything but Boom in raids and have some gold to spare, no reason not to do them.