Recently been playing 1. b3 as white with mixed results. If the bishop on b2 gets blocked it is problematic for white. 

Should I just revert to the usual 1.e4 or 1. d5  ?

if you don't have enough time to learn some 1.e4, 1.d4, 1.c4 or 1.Nf3  opening variations, 1.b3 will be ok. In terms of amount of theory 1.c4 would be the compromise to go.

Even more important: what suits your playing style best? 1.b3 2.Bb2 3.f4 (if Black didnt go for e5) 4.Nf3 5.e3 6.Be2/Bb5 7.0-0 8.Ne5 is a typical setup with play on the dark squares d4 and e5 working against pretty much everything. After 1.e4/1.d4 a lot of different types of positions will arise and you should have a plan in each, but maybe it is more exciting in the long run. If you like to attack, 1.e4/1.d4 and a later 0-0-0 might be a good choice, if you like solid positions,where neither player can crush the other soon, 1.d4/1.c4/1.Nf3 might suit better. If you like active piece play, you should check some of the main systems arising after 1.d4 Nf6 2.c4 //1.d4 d5 2.c4 // 1.e4 e5 2.Nf3/Nc3 // 1.e4 c5 2.Nf3/Nc3.

1 b3 is a decent move, but it requires subtle handling.  Even Larsen seldom used it, he played 1 g3 more often. 

You don't start out at math with calculus.  You learn algebra and geometry first.  In chess, get a good grounding in the basics of the 1 e4 and 1 d4 openings before attempting more estoreric openings.

I've seen a number of strong players--Carlssen in the 2009 World Speed Chess Championship, for instance (available on YouTube in two parts)--incorporate an early b3 as a way of not giving up their opening repetoire.  I believe the game began 1. e4 c5 2. Nf3 d6 3. b3.   I've also seen 1. e4 e5 2. Nf3 Nf6 3. a4.  There are ways to shake up main lines with alternative moves and still get a reasonable middlegame out of it.

Try the Bird opening (f4) followed by b3 whenever convenient. At first glance you might think it's got nothing to do with the Nimzo-Larsen attack, but their ideas work well together. Good early moves could be (depending on what black plays obviously), Nf3, e3/e4, b3 followed by Bb2. A good spot for the light square bishop is e2. I find this opening solid for defence as well as a great platform to launch a king side attack. Make sure you can handle From's Gambit (1.f4 e5). You also need to be careful for black's dark square bishop and queen on the a7-g1 diagonal.

After 1. b3 white is signaling his intention to play a compicated dark square game. Everything about his play must be fluid and built around clearing/controlling the center dark squares. If color domination is your thing then this is a good opening to experiment with, otherwise you will probably not have much success.

the problem with any hypermodern opening is that it leaves the central pawn structure fluid. This means that players are playing a waiting game to develop from the sidelines first then advance in the center. This relies on a great deal of experience so the correct structure can be reached. This is why you see strong grandmasters play it and do well. They are relying on their experience to outplay their opponent reaching a middlegame with the better chances. It requires subtle maneuvering on both players parts. Granted ifyou have more experience than your opponent with the ideas you can gain success but this 'soft' approach leads to problems when playing equal opposition or players more versed in the structures than you. Taking players out of book is something entirely different at the Larsen level than at the normal amateur level. 

That what i do like about it. Some guys are incredibly well read on the main opening lines of sicilian and d4 openings so the Larsen is something novel that can surprise them

your missing the point though. The idea is that when Larsen plays b3 he understands a large number of structures can aim for and is equally skilled in all of them. Infact for Larsen he was probably better than almost anyone than a literal handful of players.

By avoiding what you think is your well read opponents are playing preperation your actually just avoiding learning. (a little secret, people who think they are well read on an opening arent, I know about 8 moves of my openings but work really hard on learning the plans and ideas so I can try to find the right moves). If you think your opponents are better in a particular line pick up the challenge! learn something to challenge them back, its just a piece of the puzzle. 

TonyH I like your thoughts on this .. a lot. I want to do all I can to become a stronger player and this advice makes sense.

Thanks pfren ! .......That is an impressive Spassky game.

I think i will leave this opening to the experts.

ya thats an awesome game! classic punishment of unorthodox play and shows  spassky's brillance. People forget he was a great champion and only remember him as Fischer's lamb