Low temps will not create a stronger plant. Too low of temps will actually inhibit nute uptake. Yes it will make them purple, but I would rather have green weed that is better than purple weed that is not as good.
And how can you say that nutes only help with yeild and not with potency? What about all the nutes that are designed to increase resin production? Or think about this, does a healthy plant produce more THC than one that isn't as healthy? If you are lacking in nutes, your plants wont flower to their full potential. Yes the nutes increase yeild, but they also increase the amount of resin, reduce the amount of the leaves to bud, etc., which all increase the potency of the weed.
Also, it really looks like a deficiency to me and not a burn. Your leaves will turn crispy and grey like that from a lack of P. If it were from the lights, it would be a brown color and not grey. The grey is a sign of P def. Plus, even without proper ventilation, a small 23watt light will not do that unless it is touching the plant. I have used CFLs for years and never had them burn the plant unless they were touching the plant.