Would This Amp Be Worth The Cost?

The Musical Fidelity represents a strong value.  They are made in Taiwan (at least for now, production seems to be migrating to Canor in Slovakia) and as a result are a lot less expensive than many made in US/UK/Germany/Japan products.  Very good sounding.  Oodles of power and although a touch forward, probably less forward than that Classe.  It should be more refined as well.  You would spend a lot more and get less power (though a touch more refinement) out of a Chord Ultima 5.  It should be an excellent fit for those speakers.  
Incidentally I am a dealer for both Chord and Musical Fidelity.  I checked and that amp is in-stock at the distributor in Black.  

I love the preamp.  That is very much the digital module within the M33 and is an awesome value.  There is a surprising bias against Classic series stuff from NAD.  That is a great unit.  

I would partially agree with the sales rep.  It is not the fact that your amp is a Class D, it is that particular Classe amp is a bit older and not quite as refined as some of the more recent class D units that have been produced.  The NAD C298 would have passed it by in terms of tech and sound quality.

It isn't inherently bad, there are just amps that can give you more and if you bought it recently, you probably paid less than $1500 for it and that is an awesome amp for that price.  I sold one not that long.

That MF amp is great.  Tons of current and will have control over the drivers, just as he pointed out.  There are other options, but that amps is a strong value and is well thought in terms of pairing with your speakers.  

It will sound more natural than your Classe.  It is a great product.