In principle I agree with Bob M.
I think Bill Terry got to the point a bit faster.
No matter what monitors you get, you will have
to listen through many alternate systems
until the mixes translate consistently
to the outside world.
The one reason to change monitors is if you get
a 'perfect mix' in the studio,
but then it NEVER sounds good out of it...
So; if it's always too bassy outside
Then your speakers and/or room placement of them are too weak in the bass, so you compensate in the mix. Voila very bassy mixes.
Try moving the speakers relative to the walls, tables, corners etc.
If you CAN'T find a good spot,
that's a good sign the monitors are wrong
for the room.
If it is always muted and un-bright in the 'real world',
then your speakers are likely too strong in the high end,
(or very weak in the bass end too)
and you mix to a nice brightness,
but it is too weak outside.
So it is room placement again and/or lowering
the high end output on the speaker if it does that.
The room is a big component of your mix,
but if the monitors are pretty accurate,
then you have a shot to learn the room problems.
Most bad recordings are the interaction of a poor monitor choice for the room they are used in.
And yes decades of fine MIXES
were finalized listening on Yamaha NS-10s
but usually recorded using a wider range speaker.
And not on the NS-10s until the last stage of the mix.
It needs to work with BOTH not just the one.
All the above from all posters doesn't mean
break the bank to get speakers.
But it does mean get the best you can
and learn them in their environment.
$10k actually doesn't guaruntee you get
the right speakers for the room.
$300 can do it, but it all depends on the room.
I have mixed for 7 years on my Genelecs and matched sub-woofer,
But change the room, as I have recently done,
and it's an whole other cycle of learning the too small room.
All small rooms are an acoustics problem
and each small room a DIFFERENT problem.
So I am now building a room that takes the room
as much out of the equation as possible.
But this is barely practical for me,
let alone the average home recorder.
So that leaves the choice of monitors
and their placement to give you the
best chance to get
a good mix that travels well.
And best of luck on that...

DLD, Chili farmer. Plus bananas and papaya too.
Real happiness has no strings attached.
But pedal steels have many!