More effecient speakers?

With 150 watts on tap, you have enough power for virtually any speaker.  If you are looking for a different/improved sound, you might find it with more efficient speakers or less efficient speakers, it would not matter because you have more than enough power, so, pick according to sound preference. 

I think you have a nice complement of gear and cannot readily think of anything that would greatly improve the sound that does not involve a massive expenditure. 

To me, one of the big reasons to explore high efficiency speakers is to be able to use low-powered amps; most of the best sounding amps are low powered (under 20 watts of power).  I don't think one gains anything by getting high efficiency speakers to work with high-powered amps.  Exploring such a complete change to one's system would probably require a lot more than $3,000.

I like Mapman's suggestion about looking into a new DAC and streaming or a server.  That would not only improve sound, it would open up music that is available to you considerably.

Mapman,

Most of the high efficiency speakers I really like tend to NOT have as their forte the ability to play really loud.  Rather, they tend to sound great when playing at lower volume.  This includes some truly gigantic systems.

While not the same design, but the same designer, I much prefer the low-powered First Watt amps (I've had the J2 in my system for two weeks, I heard a friends S.I.T. amp) over any of the Pass Lab amps I've heard. 

My very favorite amps are a pushpull tube amp running 252 meshplate tubes and a custom-built 35 watt OTL amp.  The amps I own include a 6.5 watt Audio Note Kageki (parallel SET 2a3) and a custom-built pushpull 5.5 watt amp (249 output tubes).  I like both amps more than any of the high-powered solid state amps I've heard (I like high-powered tube amps even less than most solid state amps). 

But, I do think you have a good point about some new designs.  When price is a consideration, some of the reasonably priced Class D amps are decent sounding (I like Bel Canto).  These days, almost none of the better solid state designs are unpleasant sounding, they just seem a little dull and not as engaging as low-powered tube amps when playing at reasonable volume levels (higher volume is needed to make the music come alive with most solid state).