No direct personal experience, but all reviews, etc. have indicated that the stock Reserator pump is on the wimpy side, low volume, low head pressure, restrictive tubing, etc. Adding more blocks will increase the flow restriction, which will hurt flow rates and thus performance. (not to mention the extra heat added by whaterver the additional blocks are cooling) IOW, CPU and other temps will go up, hard to say how much, but will probably depend on the restrictiveness of the added plumbing. Whether that is a problem would depend on just how good the Reserator tube is at dumping heat, and how tolerant the user is of increased temps.
Changing the pump and tubing would presumably help the flow rates, but will add more pump heat and possibly increase the noise. Likewise, other reviews have suggested that the Reserator's cooling can be greatly increased by increasing the airflow over it (i.e. pointing a fan at it) but again this presumably would increase the noise. Increase the noise enough, and you can start wondering what's the point of buying that overly expensive Reserator instead of a more conventional WC system.
Building Dual Athlon MP system, Tyan mobo, U160 drives, Server Cube case, Linux ONLY, lots of other goodies. Will water cool, attempting to make as silent as possible.