The SD isn't exactly a SM with less suspension. It doesn't offer quite the same ability to mount bags if travel is your thing. The SD also has less passenger room, if you'll be ridding two up. Then there is the whole Fuel injection vs Carbs... Rear-sets vs Moto X style pegs and so forth. The great thing is you've got the choice, can't really go wrong either way.
Don't think with a 30" inseam you have to rule out the SM. Both the SD and SM use the same fork and shock. The SM can be properly lowered for less then $600 if needed. If you're handy the fork can be done by the home wrench in 4-5hrs while updating fork bushings and seals. The SD uses a spacer to lower the fork for example. A shorter rear spring should take care of the back end. With the age of the bikes you're looking at a Suspension service is overdue anyway.
I travel and ride two-up, I really wanted a SD but after test ridding both, the SMR was an easy choice at the time. May end up with a SD or SE too at some point.