It could be costly I know, level5 is a big japanese company, but after watching the success behind the layton series I think the purchase would be very worthy. After all nintendo is still swimming in money, they should use that money to either fund more internal studios or buy good studios...

 Level5 & Horii/armor project -> Nintendo should buy them asap, if not at least try to buy capcom ;)...

It makes no sense to Nintendo buy their second party studios. These guys are already developing for Nintendo and, thus, there would be little gain. Also, most of the smaller studios doesn't hold many critical IPs that would enrich Nintendo's portfolio. As such, I don't see many acquisitions among those studios, except to cover some areas where Nintendo may think they are lacking or some good opportunity, as one of the studios, pressed by bad financials, become cheap to buy it.

If anything, I would like to see Nintendo purchase Capcom. By owning Moster Hunter they would kill Vita in Japan at launch and they will got dozens of mature IPs that would complement Nintendo's catalogue nicely. Also, they could keep the Capcom brand to distribute that sort of games and thus allow NOA to release those games in America without tainting their family entertaining image they care so much.

Grasshopper Manufacture and Treasure are no-brainers for Nintendo. The others I not too sure about, Rare is a definitely no.

Platinum Games