I think that's both why they were so expensive back in the day AND why it was so hard to develop on (all I have -ever- heard about developing games for that platform).
To be fair most devs at the time completely ignored the second CPU because it was apparently very hard to make them work together. So they treated it as a single CPU console. Which kinds of defeats the purpose :)
Going by the Wikipedia description of it, they had multiplexed RAM access. So developers could choose between having two CPUs at half the RAM speed (4KiB CPU-local cache are enough to make up for it, right?) or a single CPU at full RAM speed.