More money toward better speakers or a better DAC?

Speakers... All day.

DAC technology fools/tricks people into believing the more number crunching going on results in better sound. 
Don't drink the mainstream Kool-Aid.

Speakers first... And if you get efficient enough speakers, then that opens the door to single ended triode bliss.
Or whatever class of amplification tickles your fancy.  I'm just sayin. 

after taking in all the helpful comments above, I remain perplexed but closer to a next step. 
I have b&w diamond speakers and a solid amp.  a dac will be helpful.  Bluesound node 2i dac confines the music.  
A new wrinkle above is learning the longevity of a dac can be short - 3 - 5 years? What causes a dac to deteriorate so quickly?
I believe it ain’t easy doing a great job converting digital to analogue.  
So many dacs out there and any choice requires a leap of faith.  I originally started out liking the chord tt2 and now believe this will be a great choice.  Absolutely amazed how many dacs are out there, a choice is soooo difficult.  
I liked the bartok, but it seems very overpriced.  The David seems excellent but tough to tame after purchase. I like the m scaler, which seems overpriced. And tt2 seems overpriced too.  But I want a good dac and it better last a long time.
All about feeling comfortable with a purchase.  There appears to be lots of good choices.  

People who say a DAC is for 3 - 5 years must be people who like to rotate gear. If you are into the music more than the gear a DAC can last you as long as you want. My $1580 DAC that I have now will last me until I die or it dies first. Music sounds great through it why would I change it?

I have a 20 year old SACD player, the Sony SCD-1. It is one of the best SACD players ever built. I had it modified about 15 years ago and then had to put it into storage due to lack of audio system for a few years. It is back in my new office system today and it sounds shockingly amazing. The DAC in it is not as resolving as the current DACs but the sound from that player is so addicting. It is not going anywhere. The 3 - 5 years thing does not apply to everyone.

That Chord TT2 would be a great choice. Could last you a lifetime. I am looking at the TT2 for my second mostly headphone system. Another DAC I am interested in for system #2 will be the soon to be released Luxman DACs. These should have the same conversion internals as the $16K SACD player, D-10x, but at a much lower cost. Likely in the TT2 price range.

It would have been helpful if you mentioned what DAC you were talking about. The Node2i  DAC isn't very good. The Chord TT2 is a good choice. The RME ADI-2 is a good DAC , Benchmark  DAC3 is another. you're right there are a lot of good DACs which would last you longer than 3 years. 

It is the Benchmark DAC3B in an all Benchmark system, DAC3B + HPA4 + 2 x AHB2 + Benchmark speaker cable + Benchmark StarQuad XLR (for all the Benchmark connections). My analog sources are connected by Audience AU24 SE XLR’s and RCA’s. I sold some more expensive cables to "downgrade" to the lower cost Benchmark cables.

I should add that system synergy plays a big role in my love of this system. In the past, I owned the DAC2 HGC and DAC3 HGC and it was not at the level of sound quality as the DAC3B with the other gear listed above.