I have started implementing some of the things you mention. Through a bit of trial and error I believe I now know the spine range for my rig (approx. 0.400 maybe a little less). I need to get some in this range now.
Most bows can be made to shoot a very wide range of spines accurately. I'm sure you can get .300 or .500 to work well. It just requires experimentation with draw weight, tip weight and arrow length. Just keep in mind that broadheads are more stable if the front end of the arrow is proportionately heavy. Heavy front ends require stiffer spine.
I don't have a spine tester but I really like working/experimenting with arrows. I suppose it would be worth getting. Any recommendations?
Build one, it's not very difficult. If you search the archives for "spine tester" you should find some info. Several have been made and posted on here. A search on the internet will also show you several sites detailing their construction. This is a gadget you can do without if you shoot aluminums. Supposedly there is a brand or two of carbons that are very consistant, but I haven't personally found one. You will also find it less necessary if you shoot a very heavy tip with a good helical fletch. They have less tendancy to plane.