I traded my 04-V8-all wheel drive for a 06-V8-rear wheel drive last November, and the ride of the 06 is so much better than the 04. Could be that the 06 is only rear wheel drive that might make the difference, I don't know. When I picked up the 06 it was parked next to the 04, and it was about 2 inches lower than the 04. (all wheel drive?). The mileage is a little better with the 06, but nothing to rave about.
The stock GY Eagle RSA tires on my 06 RWD V6 SRX ran horribly - noisy, thumpy, and poor wet traction. I knew the lease car was going back at 48K, so at about 30K, I replaced the tires with Michelins which ran much better.
I've never heard about any changes in suspension between 2004 and 2006. I suspect that the OP will find the ride a little different by moving from a heavier V8 to a V6 but wouldn't expect a massive difference in ride. We had a 2004 V8 and now have a 2008 V6 with the ultraview - there is no question that the '04 handled more sportily (it had MRC and lacked the top-heaviness of the heavy ultraview) than our '08 but the ride is pretty well the same.
Also, I would agree that tires do make a difference...
MRC is worth every penny regardless of any other set up you choose.
My 06 SRX V8 AWD was two vehicles ago for me, and I still miss the MRC attributes. It was not available at the time when I got my 07 lade and obviously not available on my current 09 Impala SS. The SS handles as well or better than the MRC SRX, but the SRX had the perfect balance of performance and excellent ride. With the MRC, there were no compromises that you usually get between a trade off of performance handling and excellent ride. It had them both.
Automobile(s): 2007 SRX4 N*, 2004 Infinity G35 Coupe
Re: 04 vs 06 srx
If you are looking at the ride difference, there should be little ride difference except for those related to tires, tire pressure, and suspension condition.
Tire selection for me in the past has made a significant difference in ride quality and handling. A tire pressure change of just 2 pounds could change these characteristics also, at least I noticed it every time I flip-flopped between my desire for fuel economy and handling versus a softer ride.
With suspension condition, things may all be in spec but the quality of the ride and handling is naturally going to deteriorate gradually with time and mileage, though personally I wouldn't start swapping out parts on my dime to achieve perfection. Steering racks get a little sloppy over time too. In your case, a two year difference in vehicles should not make enough of a difference.......unless you can pick up an 06 with the MRC (magnetic ride control). As others have said, that is one option worth every penny, and I wish I got it on the SRX. Every time I found one, the car was missing another one of those "must haves" options on my wish list or was the wrong color. I confined my search within 100 miles of my home outside the metro Boston area, so the used SRX inventory was always adequate.
Wife and I traded in a loaded 1998 first generation Olds Aurora with the mini-Northstar 4 liter V8 and 114K miles to get the 07 AWD SRX V8 about 3months ago. The Olds was running on original suspension, including the rear load leveller suspension. I miss that car, but the SRX is winning me over despite what downsides come with a taller and heavier vehicle.
Regarding the SRX fuel economy which is discussed heavily in the Cadillac forums.....TO ME, the difference between the V6 was heavily outweighed by the V8 punch. Neither one will win any fuel economy tests, but they both perform well enough within the market segment to make the mileage a secondary factor in something I have to drive daily. At the sacrifice of 2mpg (if that) I am rewarded every time I step on the gas "enthusiastically." My wife was adamant about the V8, so......that nixed the V6 during our search. We could have otherwise matched option for option, gotten a car for less, and could have found our colors of choice in a heartbeat. The V6 is no slouch and I could easily have chosen one and been happy.
I buy used iron and then drive to the grave. So I am one of those types that takes a long time to decide what I/we want to drive long term and then make that vehicle work for me/us. Bet I spend more time than most researching tires before I buy them.
Tires and tire pressure would therefore be my first order of business if I were you, IF the suspension is in spec. My suspension wasn't on delivery of the 07 with 26K miles. Dealer took care of that under warranty right away: both insulators on the front swaybar and both lower control arms, bushings worn. On a CPO, Cadillac dealer vehicle no less! So much for the question of what they really do on these "101 point thorough quality inspections" before they sell you the car.