Depends why you're lonely. If it's because of crippling shyness, it won't help, but if it's because you spend too much time working to cultivate a social life and/or have to live too far away from family and friends due to your career, money can potentially alleviate that.
It won't motivate you, but it will present more of an opportunity to do so by giving you more time to work with. Going to the gym in the early morning before work isn't something a lot of people want to do, nor is going to the gym after work or on a rare day off, but with more free time, going later in the day becomes an option.
That depends why you aren't content with what you own. There's a fair amount of middle ground between having necessities taken care of and having enough luxuries to have a consistently enjoyable everyday life, and while that latter goal post is very prone to being moved as people accumulate more stuff, even those who seek to practice a more modest, minimalist life can benefit from having at least a few fun things around. Greed isn't always insatiable.
Money certainly won't fix everything, no, but money does have trickle down effects that make happiness more attainable for those who are willing to seek it (mostly in the form of giving people more time to do so).
This guy gets it. I was going to make a similar post before I saw yours.