If you had a 700/ 800 watt amp (very popular and these days), it would matter, tone is very subjective and the $$$ savings is real. That said, your response is very fair for your situation.The 400w vs 250w is meaningless to me since my bass amp puts out 250w at 8ohm. When I need more, I use 2 cabs for 500w. And i'd be willing to trade off tone for weight but the difference is relatively insignificant. If they could get the weight down to 19lb or less, I'd be interested. Thus far, I have not liked any of the markbass cabs when I've played them next to the aggies...
But I agree that if you don't have any light cabs, these cabs should be in the conversation.