Image Stabilization is not necessary when using a tripod. The general consensus is that IS should be turned off when using a tripod, except for certain newer lenses which have IS systems that recognize tripod use.
Yes, a macro lens is useful for longer-distances, too, unless it is specifically labeled otherwise. A very few macro lenses cannot focus on infinity, but both Canon lenses mentioned in the opening post can focus to infinity. I specifically purchased my 100mm 2.8L Macro because it had IS, and could be used for an assignment with subjects at 600 feet and beyond, yet could also be used for quick macro shots under circumstances that preclude tripod use, such as the busy trauma room of an ER, where I try to get shots of assault-induced injuries before they are stitched and bandaged. (evidence for court) This lens is also useful for my nephew's soccer matches and swim meets. Yes, it does flowers very well, too.
My Macro L was definitely a good value for me, and I have no buyer's remorse whatsoever. Your needs and circumstances may vary. I have read reviews that tried both of the Canon 100mm macro lenses, and found no optical difference, and one reviewer said the non-L 100mm he tested was slightly better in some aspect(s) than the L. (I cannot remember the
reviewer, or what was better about the non-L.) This could well be a simple
matter of sample variation, of course. I wanted the additional benefits of
weather sealing and IS, so I bought the L.
Canon 7D/5D/40D/1D2N; Nikon F6, D700, FM3A, & Coolpix A; Canon 40mm 2.8 STM, 135L, 50L, 35L, 50mm 1.8 I, 100mm 2.8L Macro, 10-22mm EF-S, 28-135 EF, 400mm 5.6L; Nikkor 50mm 1.2 AI-S, 50mm 1.4G, 50mm 1.8D, 16mm 2.8D Fisheye, 180mm 2.8D, 100-300mm 5.6 AI-S, 18mm 2.8D, Voigtlander 90mm f/3.5 SL II