From: Vancouver, BC
When I first started playing this game, I drew the same conclusion that you have: that it was much better to concentrate your chits on a few key technologies. That is certainly true at the start for the two key combat technologies that you will need as soon as possible: Trench Warfare and Artillery Weapons (with Gas/Shell Production a close third priority). However, the longer I play this game, the more useful I find the more specialized technologies and the more I am tempted to distribute my research chits more widely and wait for results. The downside of having more than one chit in a tech is that it is an inefficient use of MPPs: once you reach the maximum for that tech, you can only buy back surplus chits at 50% of their original cost. Thus it is more cost-effective to invest only one chit per tech which will be consumed when you reach the maximum, than to invest extra chits which will get you there faster but can only be redeemed at 50% of what they cost. Plus the hard research caps mean that if you have invested extra chits in one tech, even if you have the MPPs to spend, you will often have to wait till you achieve 100% in that tech before you have the "head room" to start investing a new tech.
It all boils down to how patient or impatient you are for a given technology - or to put in another way, how much you value time versus money to get a specific combat benefit. You might decide that you need to increase your Gas/Shell production as quickly as possible, so you invest three chits in that, while you are quite content to get Long Range Aircraft eventually, so you just invest one chit there. And of course your investment strategies are likely to differ for each major, and over time, depending in part on what your opponent seems to be doing. Much of the fascination of this game lies in the different time horizons you have to apply in making choices on how to use your MPPs each turn - e.g. what capability do you need to have in the next three turns? in the next six turns? by the middle of next year?