I like the idea of having separate battery packs, a small, rechargeable low voltage one attached to the NXT to just power the electronics and another variety of multi-voltage packs (4.5, 6 & 9v?)to power the motors/ external devices. This would make it easier to build the brick into models and be able to recharge it in-situ. Having one or two sizes would let you use a pack appropriate to the size of the robot. I have a 12v portable supply which uses regulators to provide from 3v up to the full 12v so it is not impossible.
One thing I would like to see is an interface for a 4-line lcd screen, either in the brick or as an add-on. These are available for less than £10 but I find the various articles about how to connect them up confusing. I use my NXT outdoors and it can be very difficult to read the standard screen. This could be attached when setting up the brick then removed before using it. Either that or add a backlight to the existing screen and add the options for large text as part of the standard firmware.
Re the cost of sets, I have bought 3 complete version 1.0 sets through ebay, lowest price was £80 and highest £110, all including p&p. Used but complete and in excellent condition. Getting one that way then buying the extras needed to bring it up to version 2 inventory is fairly cost-effective.
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