"Exploits" of tech trading in Civ4 are often overestimated. Many have followed some Deity forum games and seen some really good player getting 5 techs by trading one. It may look like a cheap exploit, but they don't realize how much planning that kind of "exploit" needs and that it has risks too (one AI may get the tech you're beelining and trade it to everyone - you're getting nothing of your beeline). RAs, on the other hand, were guaranteed to give you a tech you wanted if only you were willing to do tedious but quite no-brainer calculating of blocking right techs at a right time. It was much more exploitable than tech trading ever was. Furthermore, RA is a fundamentally silly concept. Tech trading is a clear (while not realistic) concept - you give a tech and you get a tech, but RA don't make any sense in real world and just gets more and more confusing when they try to fix it. Your lump sum solution would be better than it's now, but it would still offer an automatic no-brainer exploit for a player. He would simply have to make as much RAs as possible with as many AIs as possible to grant maximum RA beakers for him.