I did pay a (net) $50 to Sherwin Williams for them to send their color consultant out and help me pick colors for pretty much the entire house. Very much worth the money, since I'd spent 2 years trying at that point.
I decorate to meet my needs and comforts, with things I like. If others don't like it, too bad. I didn't pick my wall art with you in mind. The end result is a bit odd. But then, so am I.
Absolutely, getting a paint consult is completely worth the money. However, a lot of places will do them for free where I live if you buy enough paint for a whole house.
These consults are worth it, not so much to help you pick colours, but to help you pick the right tone to achieve the colour that you want in your particular space.
I knew exactly which colours I wanted, but the colour consultant saved me a world of pain by translating my swatch vision to what would actually achieve it on my walls, such as picking a grey that I thought would be too purple, but ended up exactly right.
However, for actual interior design, I think it's overkill to hire a professional unless you really, really want your home to look like a magazine. A lot of my friends hire decorators/designers, and I rarely like the outcome, and it often ends up feeling hotel-y, because that's been the prevailing trend for soooooo long.
Take your time, look at lots of photos, and build towards a style that you like. But focus primarily on function, not form, because this is what you need to live in. As people have said, start with the most expensive or most important furniture items, and then work from there.
That said, if you want a decorator then hire a decorator. What's worth it to you is up to you. If you truly feel hopeless at decorating and are certain that you will end up with a tacky hodgepodge of expensive furniture that you hate, then go ahead and hire some help.
As much as I've seen a lot of what I consider to be tacky, overly designed rooms, I've also seen a ton of, well, downright awful furniture arrangement and styles where it's truly a god damn mess, and could have been avoided with some advice.
Do whatever works for you.