Unless you're good at investing, and/or have some ability to invest your marginal dollars in a
tax-advantaged way, it seems unlikely that investing will really generate you much money. Your numbers, though, suggest that you are exceptionally good at investing, and can turn less than $17,800 into an income of $2400 per year. That's at least a return of 13.5%. If you can regularly earn a return of 13.5%, reading my comment is a waste of your time.
Your scenario involves paying off the loan quickly vs slowly, and also the factor that some of your money would allow what appears to be a leveraged real estate investment. Without all of the details, it's hard to compare the two scenarios you have mentioned.
Perhaps this scenario will be helpful in your decision making: imagine you have both $17,800 in cash, AND a reliable post-tax cash flow of $392/mo for the next four years. The choices then are A) Pay off the car with the $17,800 in cash, and invest the $392/mo for the next four years. or B) Invest the $17,800 now and use the $392/mo to make the car payments.
Imagine that you could earn 6.5% like George, and that you are also subject to a marginal tax of 34%. Over the 4 year term, you might end up with around $604 total additional money with choice B (A=20,453, B=21,057). Naturally, if you can earn greater than 6.5%, or pay less than 34% in taxes, you'll end up with more money. If you factor in the insurance savings described above, you'll end up with less, etc... We also haven't factored in inflation, and that is an incredibly interesting, but complex consideration that is highly dependent on the individual.
These questions of pay now vs. invest and borrow come up a lot. The standard response is to quickly consider the difference in the loan interest rate and the pre-tax investment return rate and punch out a quick answer. Minimal consideration is given to the real, post-tax difference in wealth at the end of the two scenarios.
Generally speaking, for amounts under $50k, terms under 7 years, and differences in interest vs return of less than 5% (without accounting for taxes), usually the answer is: it doesn't really matter. How much effort/risk should a person with $18k in the bank and a $400/mo cashflow put into earning an additional $600 over four years? Lastly, issues of significant consequence are often entirely left out of the equation-- such as the insurance savings of paying off the car earlier.