The OEM droplinks should be more than adequate. What other mods were on your car? Where you using Semi slicks?
You would only need more articulation/movement in the droplink if your were putting it under extreme load it wasnt designed for. Open Bearing designed ones should also be perfectly fine for what their designed for, however they would require more maintenance to keep them clean and well lubed. Something which i mentioned should only be considered if your tracking your car and if your doing that you would strip your suspension down often anyway. The open bearing ones would be alittle extreme, but if im honest i'd imagine them being better for "racing use" due to the direct nature they will transfer the load.
Im not saying the Powergrid ones are bad, in fact they look very good. But the fact is, for majority of people on here that use their cars on the public road they probably havn't had a problem with the OEM droplinks and could if they wanted replace 3-4 of them before the cost of a Powergrid ones (only 2 bolts to replace them too). Now the powergrid droplinks aren't a fit and forget item as just like the OEM droplinks they have a rubber bush which WILL perish over time. Obviously they'll last a while but so should the OEM droplinks.
My 350z had done over 60k miles IIRC and i never had one problem with the droplinks. If what you say is true, either the user's are putting them under extreme load, (hitting curbs on track, potholes) etc.. or Nissan have badly designed what is in essence a simple item. Your right in the fact that they do break, in fact my current car is prone for it, but if they break every 2 years im happy paying the £37 or less to have it replaced which does its job perfectly well.
If they've broke or the car has high mileage then it may be worth considering swapping to the Powerdgrid/similar ones, but certainly not if the bushes are fine and their in good condtion.
Dont fix what isnt broke. All in my humble opinion of course