Sorry, I don't seem to follow you regarding RAM. A quick check on Scan.co.uk shows the cheapest 2x4GB 1600MHz RAM at about £40 (Corsair Vengeance Blue 9-9-9-24) which is reasonable. Then the cheapest 4x4GB 1600MHz RAM is £81 (Corsair Vengeance Jet Black 9-9-9-24), double the price. A 2x8GB kit (Corsair XMS3 11-11-11-30) is about £89.
If he had the money lying about, burning a hole in his pocket, then why not? Get 16GB. But for those that want the most bang-for-buck with a limited budget, that extra £40 can easily pay for a case, or would be better spent ADDED onto the case budget. Or a CPU cooler and some fans. Or an active display adapter for tri-monitor setups. The performance difference of 8GB vs 16GB is measureable, but the meager difference is not worth the £40 asking price IMHO.
So unless we move from DDR3 to DDR4 or something different within the next 2-3 years, I think 8GB is a safe spot for the near future. Good enough for today with the possibility of upgrades in the future. The only time I had that RAM issue you are describing is when people are stuck with motherboards with DDR2 RAM and DDR3 became cheaper than DDR2. I even had a friend who made his DDR PC last for some time, only to find out that we've moved on to DDR3 and he was then looking at a mobo, CPU, RAM and GPU upgrade... but by then his PC was ancient anyway
Regarding overclocking, I just want to make it clear that it is a hobby for some, but not for me. I did it because I wanted to learn it and decide for myself if it was worth the risk... I did tests, recorded the numbers, then tested some more. As my CPU is said to be "safe" up to temps of 80-100 degrees and my toughest burn test only scratched 80 and my toughest GAMING test (DCS A10C, Skyrim) brought only about 60 degrees, I decided it was worth it. My analogy is like driving a car... you know your limit, you know your car's limit... why putter around at 40mph when you know you can SAFELY do 60mph and that your car can take 80-90mph easy? So what I am saying is learn how to overclock, do it, do it carefully (the guys at overclockers.com are very patient and helpful!), keep good records, and see what your PC's limits are using the stress tests designed for overclocking. Once you are there, see how your toughest programs and games are stressing your PC and how far you are from your PC's limits. Then make an informed decision whether it is worth the risk or not.
Most of the bad rep of overclocking is coming from guys who ask for too much from their system, frying their CPUs due to forcing it to go to 4.6GHz when it can only do 4.2 just because he read about some other guy somewhere that got 4.6GHz on roughly the same setup as he had... pfft! Darwin award! Each PC is different, even if the "specs" are the same. It could be as little as what type of silicone grease used, or the technique of applying the CPU cooler, or the airflow inside the case, or the ambient room temperature at the time of testing... that is why I recommend to learn how to do it, test, record, test some more, THEN decide based on your own experience and test results.
Practical side --- you know your PC's limits. If your PC starts acting up, you can do your tests again, see if something is wrong somewhere. Is your PC running hotter than before even on idle? Is it running hotter on load? Run your old stress tests and program tests, is it still generating the same numbers or are those off as well?
Practical side --- you get a little more from your hardware for just a little time spent tweaking. Two weekends experimenting for a jump from 2.6GHz stock to 4.2GHz maximum stable overclock, then moved to 4.1GHz for "safety." When games and programs today still not being optimized to use ALL cores and when clock speed still mostly wins over number of cores, you can see why it I think it is worth learning this limit and getting what you can safely get.
While you are 100% correct that overclocking is sending more power to the hardware making it run hotter == shorter lifespan, note that I do not recommend blind overclocking but rather a careful, measured, and educated approach towards the limits. As such, some rules SIMPLY HAVE TO BE followed. Do not overclock using the stock cooler. Do not overclock with big jumps in settings or changing multiple settings at a time. Do not overclock without recording your results. Keep good notes, etc. etc. I have so far added about 0.1375v to my power settings to get almost double my clock speed while safely staying on reasonable temps. Hotter? Yes, slightly. Shorter lifespan? Probably, but only by a little if any. Also see my recommendations for proper airflow and cooling within the case.
Is this useful for home users? Not if your toughest stress test is Facebook and video editing for that Friday presentation. But for simmers and gamers like us, I think if you can get that extra oomph at reasonable risk, why not?
Sorry for the long post, I do not mean to argue, just an educated debate, but I am simply presenting my side for whatever help it can offer.