Just thinking about this, it all seems pretty silly. A 1998 CR-V gets EPA rated 19/23. Say you spend $10k to buy a car that gets 30/40.... $6k differential since you sold the CR-V for $4k. So you're getting 11MPG more in the city, and 17MPG more on the highway. Let's split the difference and say that you get 14MPG more on average, so let's peg the average fuel economy in the CR-V at 21 and the new car at 35. Now let's say that you drive 10k miles per year.
10k miles at 21MPG is 476 gallons of gas. 10k miles at 35MPG is 286 gallons of gas. That is a difference of 190 gallons. Multiply 190 gallons times $4/gallon and you get a grand total of savings of.... *drumroll* $760 per year. Take gas at $5/gallon, you're still under $1000/year. Double the driving to 20k miles per year, and you're looking at roughly $1500 a year. At the 20k/year level, you will have to drive the new car for 4 years before you break even with the $6k that you spent to buy it. Not to mention, your CR-V has surely already depreciated almost as much as it's going to, while the newer car will have a lot of depreciation still ahead of it. So tack on another couple of years for depreciation.
Of course, there are intangibles and other benefits from having a newer car. If you want a newer/smaller car, that is certainly your prerogative. But trying to make it all about gas mileage is just fooling yourself. Penny wise, and pound foolish. You could see how small the difference was even with a major (67%) MPG improvement from 21 to 35.... trying to split hairs with the cars that you're considering (e.g. 38MPG for Car A, vs. 35MPG for Car B) is a waste of time and money. Get what you want, get what appeals to you, and don't go for something you don't like just to save a few bucks on gas, because that's all it is, a few bucks (when compared to the cost of the car). (Unless you do a truly large amount of driving, like 40K a year, which I doubt you do since you've been driving a '98 CR-V.)