Before you spend more money on something you may already own....I am looking into a new way of using Space Designer involving sending from individual instruments on PREFADE aux sends rather than post. This means setting up a bus or aux object with Space Designer operating with no direct signal and full reverb. Thus the balance of dry to wet will depend on each individual instruments fader settings and aux send settings. The room has to be absolutely right, but audition plenty of them and there are some peaches. Try for example Magic voices in Vocal Rooms>Long. The effect of having purely wet reverb sends thanks to the pre fade and not post fade send seems to be that you are not simply adding reverb, but placing the sound back into the reverb. my initial experiments are startling good. BUT THE ROOM HAS TO BE RIGHT!
By all means buy altiverb, but, personally, having recently slated Space Designer, I am now beginning to love it, AND IT IS INCLUDED WITH LOGIC!