Is it worth it? Fox 36 to a 38?

I weight 180lb and find the 38 a much better fork. I think 38 is a great middle ground of stiffness and compliance. I think the extra stiffness also helps the fork perform better as it slides through the bushings.

At 280 lbs your best bet if you want more rigidity is a double crown fork. Likely the added stanchion stiffness of the 38 won't make much of a difference, it will just move flexion more towards the crown/headtube joint. I am pretty sure a RS Boxxer isn't much heavier than a 38. 

on a switchblade though? you're only going to be able to make a 160/142 bike so aggressive.  A shortened 38 or similar fork is probably the best option if it's additional stiffness needed and not tuning related.

It'd likely help with the front end stiffness, but there could be other options to consider.  I can't relate with your size and impact on the front end.  At half your size I do notice the Zeb is stiffer than my 36 is all I can say.  

Your wheels could be causing the flex feeling you get as well.  Something like the EX1700 vs the current XM1700 may be a better option.  Or a stiffer carbon wheel.  If you are noticing the flex front and rear this might help more than adding the 38 to the front.  Trading out the wheels while they are newer and selling may be good before you egg them off some rocks and they lose value.

If it it feeling squirmy side to side on harder turns, tires could be causing some flex.  Your bike comes EXO+, and you might benefit from adding a stiffer insert to both tires (cushcore or rimpact) or adding DD casing front and rear.  Being in AZ with rocks and bigger guy, this could help in the long run and is the least expensive option. 

If you are diving through the travel on a straight line it might be a tuning issue.  I have found the DSD Runt improved mid stroke support during repeated hits in situations like this.  

You're probably OK on tires, especially if you have them at higher pressures.  I use the SRAM guide as a starting point https://axs.sram.com/guides/tire/pressure which tells me you could be somewhere in 29-33psi. 

I haven’t ridden the current Gen 36 but I swapped from the previous gen lyrik to the 38 it was eye opening. I’m 240lbs ride on the faster more aggressive side and noticed the change on the first ride. Less deflection on hard landings and I really like how you can tune the air spring to get it to ride just how you like. Just my 2c as a bigger guy.

I rode a Switchblade with a 36 for a couple of years and a Stumpjumper Evo with one after that. I weigh around 225lbs with an aggressive riding style and can relate to the feeling of that fork flexing under heavy braking, especially while changing direction in the rocky terrain here in Arizona. That was the only real issue I had with the 36 on the Switchblade, on the Evo I experienced a bit of a binding issue with the slack head tube angle (64.5 degree) that created an inconsistent feeling on trail. I opted for a Zeb over the 36 on my current Stumpjumper Evo and it's alleviated those binding/twisting issues I experienced previously. I've ridden quite a few Fox 38s and it's slightly stiffer than the Zeb, so I think you'll notice a bit more feedback in your hands from the rigidity of the chassis but also notice damping stays more consistent through varied terrain. In my experience, the benefit of consistent damping and staying more composed on trail outweighs that drawbacks of weight and feedback at your hands.