This thread is way old, and I imagine the OP has long ago made a decision, but I'll throw in my $.02 anyways. I have a Mark II 22/45 with the stainless bull barrel as well. I was also not happy with the stock sights, but just happened to see some on Ruger's website store. It's a fiber optic front sight (includes two colors, three sizes each) and a V-notch rear sight blade to replace the stocker. The combo was $50.
Visibility with the new sights was MUCH improved. In outdoor natural light, the front sight glows like a neon sign! Even fairly dim natural light will still work quite well. However the effect is not as great indoors. I like the "lollipop" sight picture this combo creates... just line the big yellow/green (or orange/red) dot on the verticle white "stick" and pull the trigger.
But if even 'souped up' sights are not what you're after, I recently read a pretty glowing review of Browning's red dot sight for the Buckmark series, which I'd imagine you could mount on a Ruger. Price was about $50 and the reviewer said it worked like a champ on his Buckmark. Might be worth a look.