Yes, toeing in and out your speakers can have positive (and negative) effects, but it is also dependent on what speakers you have, your room size and shape, ceiling height, whether you have hardwood or carpeting, as well as any other soft or hard reflecting surfaces in your listening room (hard cabinets and soft sofas for instance). Don't fret however, as every room is different, and it all boils down to adapting to your room's specific parameters and dimensions.

You can also try things like tilting your speakers (front and back, start with very shallow angles), as well as actually
raising your speakers beyond what most would widely consider to be an "optimal" height (generally most would say the tweeter should always be at ear level at your listening position). Just hear me out: I know this is a highly unorthodox approach, but I have heard speakers absolutely come alive by raising them above ear level to heights that most would consider "too high" or generally above their "optimal" listening height. By doing so it can also add more definition to the bottom-end, and lead to a more cohesive sound with more air around instruments, etc. Some may say, "Well, just try listening to your speakers at a lower seating position, and you will get the same effect", but they are overlooking the actual physics of what raising your speakers does. There is also a dynamic that exists of how certain frequencies bounce off the floor, and how it affects and colors the sound. After all, the floor makes up a part of your room's sound as well. You can sit lower, and it
will change the sound, however the
actual sound/floor dynamic is unchanged because the speaker is still at the same height in relation to the floor. The only way to change this dynamic is to raise the speakers up beyond their current height. This won't be beneficial in
every scenario, but it can work more often than many people would ever give it credit for. Try anywhere in the 6-18 inch (15-45 cm) range. Try incremental heights to see what each height does for the sound. Try it out to see if it works for you, and if it doesn't, it won't cost you a thing to experiment.

I know this is more difficult to do with a pair of floorstanders, and that raising floorstanding speakers to those heights would probably be seen as highly unorthodox for 99.9% of most people reading this, but there is also a
height dynamic that exists in regards to your sound as well, and that dynamic can only be changed by raising your speakers. Bookshelf speakers aren't the only speakers that can benefit from adjusting height. Just try it out. Like I said, it won't cost you anything.
Also, if you are looking to buy a sub, I would also highly suggest buying an isolation platform similar to an Auralex SubDude HD sound isolation riser for it. Isolating and decoupling it from your floor does wonders for the bass performance of your sub and your system as a whole. It will also increase the soundstage, and it will give you a tighter and more controlled bass performance - regardless of any "faults" your room may have. It also goes without mention that speaker floor spikes help to prevent and decouple them from adding, and being affected by floor vibrations. However, the very least I can suggest is if you buy a sub and don't try anything else, buy an isolation platform for it. It will do wonders for your system's overall performance. But with that said, try raising those speakers!

That's my two cents. Happy experimenting!
BTW, I also have a very quick way to optimize sub placement that works wonders for any room - regardless of its size or dimensions. It is a method that saves a ton of time, yet will help to fully optimize the sub's placement for your room in a very direct and meaningful way in relation to your preferred seating position - no matter where that position is within our room. Just let me know if you are interested to hear about it. Cheers.
