Upgrade Mordaunt Short Premiere 5.1 speakers to Dali Spektors? Worth it?

[NeilF]

So I have a rather old 5.1 package of Mordaunt Short Premiere speakers, which I upgraded the front pair of:-

• Front: 902i - -MORDAUNT SHORT AVANT 902i SPEAKERS
• Rear: 302 - -MORDAUNT SHORT PREMIER MS302 SPEAKERS (PAIR)
• Center: 304 - -Mordaunt Short MS304 Centre Speaker Cherry (Open Box)
• Sub: 308W - -MORDAUNT SHORT PREMIER MS308W SUB WOOFER VANADIUM

And this is all working through my Onkyo TX-NR646 amp and I listen to a mix of music and home theatre etc.

Three considerations:-

• The current front 902 speakers are quite deep, with one on a shelf, very very close to the rear of the unit. Not ideal (being rear ported)!
• I feel the center speaker maybe isn't as good as it could be. It's in a dedicated shelf immediately below the TV, and there's enough room to fit a bigger speaker in there.
• The woofer feels a tad disconnected, if that's a good term. It doesn't feel tied/combined into audio at times, almost like it's not controlled enough?

So after looking around I'm wonder if a Dali Spektor speaker setup might be the answer?

• Front: Spektor 1 or if really worth while the 2s - The 2s are 3cm less deep than my existing fronts, so would give an inch more of space on that shelf at the rear. The 1s would give loads more rear space, so would be the more logical choice space wise.
• Rear: Spektor 1
• Center: Spektor Vokal
• Sub: C-8 D (down firing) or E-9 F (front firing)

In people's opinion, is that going to give me a good solid noticable improvement in audio quality over my old Mordaunt Short speaker package? Is it going to be £900 or so well spent? ie: Might nightmare would be little/no real improvement.