That's not a bad "free" upgrade, if for no other reason than to get the latest generation processor..................
Since you haven't been overclocking, then heat shouldn't be any more of a concern than it was before. Yes, Ivy and Haswell are hotter running chips - especially when you start overclocking them and putting more juice to the cores. But core to core and clock to clock Ivy and Haswell are better performers and more efficient.
The primary reason for the temperature differences was Intel's decision to change the mfg. process as it concerns affixing the IHS to the die. On the SB chips they used solder to create the thermal "joint" between the IHS and the core. On Ivy and Haswell they went to a thermal paste (which based on some of the videos and pics I've seen of delidded 3770Ks - isn't the best stuff in the world).
I don't think I would pay new retail to jump from Sandy to Ivy or Haswell for a desktop PC, but if I were getting a good deal used or even better a "free" upgrade, I think that is a no-brainer. Keep in mind that Haswell requires a new socket, hence a new motherboard - socket 1150. But the SB and IB both use Socket 1155, so are interchangeable for the most part as long as you have a motherboard revision and BIOS that supports IB in addition to SB.