No mpg loss from empty roof rack
Your experience differs from mine. I get no mpg loss whatsoever from driving around with empty crossbars.
What happens to mpg evidently differs greatly, depending on the size/shape/weight/power of the vehicle involved. Mine’s not exactly aero or lightweight in the first place. Adding some crossbars does absolutely nothing to the mileage.
Adding a kayak on top…we shall see. Too soon to tell yet. Nothing obvious so far.
Thanks for the tips
Definitely lots of things to think about. A guy I work with has a rack on his truck and I will ask him about it too.
Well put and a good summary
Since this subject comes up about once a month here year in and year out, you need to keeps this summary and post it each time someone asks.
Cheers,
jackL
Prices
$600 is an overestimate, at least for my car. ORSracksdirect.com has good prices, but I assume most online prices are about the same. Their website does have a good system for making sure you get the right setup for your particular car model. A complete Yakima or Thule system for a Prius comes to about $310 to $320; ($50 more if you want hully rollers rather than regular saddles at both ends; $50 or $60 less for a Subaru with its own factory rack).
$300+ is still a lot of money, of course!
Saris racks do work well
I’ll second the Saris recommendation. I keep the saddles mounted on the racks. When I need to transport, the racks install on my car in a couple of minutes.
Antenna
The antenna in the back isn’t a problem if you don’t center the kayak rack on the center. If you are carrying two kayaks, the kayaks sit to either side of the antenna.
Second Boatloader Extension Tube
I have one on my Yakima setup. I’ve been happy with my Yakima. I have two kayaks about 40 punds each that I can load by myself even with a bad shoulder and a 6 foot roofline. I have a Honda Element, so the roof antenna is there, but I load on the other side of the roof, so it isn’t a problem. I’ve never put two boats on top to know if it would be a problem. I have never damaged my car taking the boats on and off. But, Honda was thoughtful enough to put plastic on the roof edge, so YMMV with a painted edge there. I haven’t noticed any gas mileage difference with an empty rack (crossbars only) but do with empty saddles or a boat on top. Of course, the Element isn’t an aerodynamic masterpiece itself. I have the Yakima pads on the front bar and pipe foam on the back bar. Quite frankly, I like the foam better. I leave the pads on all the time to cut down on noise, too.
BTW, I think roof racks look good on cars. I always make fun of SUV’s that don’t have racks, especially when I have a boat on top and bikes on my (Saris) hitch rack. My car has more fun 
I guess it depends on the width
My kayak is very wide (31 inches). At its widest point, about the middle third of the boat. I have not measured the distance between the edge of the roof and the location of the antenna so I don’t know if it is an issue really. It is something I was wondering. The alternative is to carry the kayak on its side.
Probably not a popular opinion
but I would try to keep the Nissan if you like it. Im not saying dont buy the Mazda, Im just saying, can you swing two vehicles.
Personally I would never mount a rack on a brand new car. I know many people do it, but I wouldnt. It can be hard on the finish and hard on the sheetmetal if everything isnt done just right. I feel the same way about bras and those rooftop cargo bags also. I wouldnt feel very good about taking a new car to some of the put ins around here or dragging mud, sand and water into a new car. Thats just me, I suppose most people dont care.
The good news is, and has already been stated, most of the roof racks only take a few minutes to put on and take off.
The Mazda doesnt have a factory rack so you will need an aftermarket rack that will probably have rubber feet that rest on your roof, with straps that clamp into the door sills.