Hi Bill,
You just described my experiences with the BIG rides at WDW; I'll do Space Mountain, Splash Mountain, and Big Thunder Mountain, but I'm terrified of Tower of Terror and Rock 'n Roller Coaster (I have been on both of them, though). However, my husband and youngest son could ride the two at Disney's Hollywood Studios over and over. They really are different attractions with different intensities.
I will usually do Expedition Everest one time, but then I'm done while my sons can ride repeatedly; they have actually ridden it four times in a row. So there is really no rhyme or reason to what rides guests will like or be afraid of. To help with your decision making if you want to try them, here are a couple of differences (which could possibly be spoilers):
Expedition Everest: goes backwards, feels like you go upside down in the dark, too
Tower of Terror: totally different sensation as you anticipate the drop (many ride variations) as well as the dropping sensation
Rock 'n Roller Coaster: 10 second countdown as you take off builds anticipation and then goes VERY fast within seconds and has loops where you will be upside down
And as for Mission Space, I have to confess I got into the vehicle this summer and freaked out (I'm claustrophobic). Thankfully, the cast members do check on guests to make sure they are good to go before the attraction begins, so I thankfully was able to make a quick exit. My sons love this ride, and it does offer two levels of intensity. You could begin with the green side which is less intense (no spinning) and work your up to the orange level if you'd like.
If you'd like to read more about the attractions, please visit
here. I hope this helps you to decide if you're up for the new experiences. As for me, I'm going to stick to shopping while my sons have the fun!