Steve, you can always add roses between the roses already there. Prune heavily in the spring so you can see how much space you have and add something new. You could also put on the mulch heavily at that time. I bet if you mulched with straw, it would improve your soil and really help with keeping the moisture.
It doesn't work with all roses. Some are just space hogs and there is northing you can do about that. For instance I used to have Austins GOLDEN CELEBRATION. A Lovely rose but it wants to be big and just will not stay smaller. I replaced it with GOLDEN ZEST a Jackson and Perkins english style rose that is similiar looking but much better behaved.
