Funny but although i'm only just startin out in AV, the 2 speakers mentioned are 2 i've actually heard. I have the yamaha in a second lounge and as said they are ok as a starter set. Auditioned the alumnis last week and they are in a different league to the yamahas.
I recently made the same move, from NSP110's to the Alumni's and have them connected to a Yamaha DSP759SE amp.
The Alumni's are obviously a step up, sounding more open, detailed and with much better integration (especially with the sub - which now 'thuds' rather than 'booms' if you know what I mean ). They produce a really good/wide soundstage compared to the NSP's and are far better with music. Surround sounds are better 'placed' (I always found my rear speakers were lacking with the NSP's) and when combined with a much clearer and more capable centre makes for a great/involving movie viewing experience.
I've not read anything negative about the Alumni's apart from the very slight criticism that they aren't the best for music - although I am happy with their stereo playback.