I'm an enthusiastic user of Reality/Luxrender—in fact I use nothing else. I have a powerful graphics workstation so graphics capabilities and memory are not an issue. Nevertheless I will not consider using GPU acceleration because of its limitations. In fact it can create more noise than is compensated by its efficiency, and there are a number of other issues, some obvious (e.g. limitation of GPU memory), some less so. The best way to increase efficiency is careful use of lighting. For example, use only mesh lights (and I rarely need more than two of these) and enclose your scene in a cube primitive to reduce wasted sampling. If you observe such techniques renders can be remarkably efficient without GPU contributions.

Having a 32 bit system certainly limits your capabilities. I had such a system until quite recently. I had to become resigned to being able to render limited scenes. I didn't find GPU rendering (although I had a decent card) much help with this.