I think the most important part of the question is not kit, ARF or RTF. The greatest change for the mainstream in this hobby is going to be mode of propulsion!

Electric power, in my opinion, will overtake glow in the next five years. If the advances in battery technology and motors we have seen in the past couple of years continue and prices continue to drop there will be little reason to consider glow power for anything other than special applications. In five to ten years your sport 46 glow engine may be a dinosaur.

Having said this, I am just starting with medium power electrics and am dealing with battery weight (NiMH rather than LiPo), charging considerations and a relatively high initial cost. Performance costs money and I am probably going to have to settle for less than ideal power at this stage. The battery cost is probably similar to the cost of the fuel it replaces but there is significant up-front investment. I am looking forward to MUCH less noise and not having to clean the slime from my airplane at the end of the day. Also just starting the learning process and will, no doubt, continue to fly glow for some time to come.

No matter if you build (kit), assemble (ARF), or fly out of the box (RTF) this is a great hobby with more than enough variety to keep anyone interested for a long time.

Ross