The tubular K-members are not necessarily stronger; their big selling point is that they are lighter.  A lot of them move the wheels and change the car's wheelbase.  Others are hard to install and have a lot of bad reviews.  The MM ones are great, but they are also pretty spendy.  The cheap ones you see for like $300 almost all have bad reviews, except G-Force I think.

Once you do the subframes and the strut tower there isn't a ton more you can do short of a roll cage.  The K-member braces are cheap enough to give a try maybe.  I'd probably do that long before swapping the whole K-member. 

I'm trying to come up with a way to install a roll cage that's not to invasive. I think the only way it will help is if I can tie it into the "A" pillar at the top and about half way down, and then to the sub frame.  I don't want it to take away from the car or make the back seat unusable.

I've seen some custom built cages over the years that fit really tight.  A proper cage has triangulation, but that triangulation also hinders rear seat access, etc.  You can make swing out door bars, which still add to stiffness, though obviously not as much as permanently welded ones. 

I'm thinking DC is on to the best first attempt, I presently have the Maximum Motorsports Strut tower brace, 

Not my car but this is the brace I have.


It looks like this,


I could modify mine to be more like this one,

And I could add a brace that would connect to the cowl back at the hod hinge supports.