I've got my (threaded) stem at the maximum height, but I'd be more comfortable if the bars were higher relative to the seat. It would be uncomfortable to lower the seat any further.
I was intrigued by the idea of a stem riser as a cheaper solution than a taller stem, or a larger frame.
Stem risers do work but have limitations. They increase the amount of force you can put on the headset (as does anything else that gets the handlebars further up), they can break (unlikely but possible), they add a little slop and they often creak (a consequence of the slop). If you're a strong guy with wide handlebars and you're prone to really grunting on the bars you're more likely to break a riser (or anything else), and will probably find the small amount of extra slop makes the bars feel loose (or as though they're about to break).
threadless: 
quill: 
I've generally suggested them as an interim solution for someone playing with bike fit, or for someone who wants a bigger frame but can't afford a new bike.
Right now I have a back injury that means I need a more upright riding position, and I've obtained that via a set of upright bars that have a bit of rise as well as the sweep back, and a stem with more rise (that I swapped off my old commuter bike).
In addition to Moz's answer, with which I agree, a stem riser can affect the handling of a bike, and it's safety. In most cases, they are fine and perfectly safe. Any thing like this can be carried too far, however, and your frame is designed with particular limits on the amount of leverage placed on any part of the frame. There are always extra margins built in for safety, but carrying any kind of modification to the design of a frame TOO far can result in damage.
Also, too large a change can, depending on body proportion, put you in position that will pull you too far toward the rear of the frame. That change of balance can make the bike steer "skittishly" or "lightly", because there is not a balanced proportion of the weight on the front wheel (which handles your steering).
Meaning that a 1"--3" riser is probably fine, but installing a 10" riser is probably not.
Given funds and opportunity, you are in the long run better off getting a frame that is fit correctly, or a style of bicycle better suited to your needs. IMHO.
I am agreed with @zenbike + @moz and I have part-covered some of the gotchas of this topic already.
What you might also like to try are some 'North Road' style handlebars. These will bring your arms into a more relaxed posture whilst still enabling you to put some weight onto the bars. Typical 'North Road' bars do rise a bit, bringing the hands closer helps too:
You can try before you buy as lots of bikes have this style and a short ride with them might have you convinced.
