Using your body to attack the attack

Seems like a dangerous strategy to me?

I for one would rather avoid the point of direct attack and concentrate on counter-attacking potentially undefended areas of the body, or re-direct force, or make use of an attackers potential lack of balance etc.

"Attack the attack" at it's most direct level, no - with my judo head on that is just hardness vs. hardness, and not maximally efficient. I would much prefer "softness overcoming hardness".

I believe Paul Vunak teaches elbow strikes to incoming punches. I tried it once in practice. I would need a lot more practice to make it work live. I prefer the FMA use of gunting - strikes to muscle mass in the attacking arm that results in various degrees of limb destruction. Obviously that requires getting out of the way of the strike on its way in. It also isn't limited to the arm.

From the various kung fu styles I've picked up numerous uses of body bumping for in-fighting, whether head butts, elbows and knees, or slamming the trunk of the body into the attacker. The latter also being a variation of some of the aikijutsu I used to train.

Headbutt into an ancoming punch? Not for me.

Yes I do some of these things, but generally not as a preference.

1. elbow to incoming punch (straight punches only)
2. knee to incoming round kick (into thigh)
3. elbow to incoming round midsection kick (into shin)

They certianly work in the right situation, technically they can be difficult and you have to be resilient in terms of not damaging yourself in the process, but sometimes we don't 'choose' what to do - survival can be painful!

In a way, but I wouldn't go directly into an oncoming attack if it could be avoided. I just think it would be too risky to be worth trying. For example, while it is true that against you average person headbutting their fist might break their hand or fingers, it also risks a concussion. In my opinion it is easier to keep fighting effectively with a broken hand rather than with a concussion -especially while pumped on adrenaline. Not to mention what could happen if they have a weapon in that hand... The only benefits to that I can see are that A: His mates will probably think you're a complete psycho and B: "Judge, he headbutted my fist and broke my hand" is unlikely to fly in court should he decide to sue you

I think moving into an attack at an angle and attacking the limb can be very effective if you train and condition for it, espeically if you target a vulnerable muscle or joint, e.g. preemptively stepping into a roundhouse kick before it can develop power and attacking the knee or unbalancing the opponent. I would do this at an angle whenever possible rather than going straight into the attack though, to reduce the risk. 

Basically I think about it this way: If I had a chance to do it against a really strong striker or someone holding a weapon without mauling myself horribly, it might work. Otherwise I would consider the risk to great. But that's just my opinion, influenced by my training, so different things might work for you

I've taught the idea of pushing your stomach in after a kick on the expectation of taking and pushing back an opponent's punch, but that's purely conditioning and/or a preparation for if it all goes pear shaped on the block.     I've also seen the effect of shin on shin from people who didn't kick trees for a living and it wasn't pretty so I'd not be risking mine.

Personally, I'd avoid as much as possible and if I used a strike against a strke it wouldn't be force on force, I'd be looking to hit something of the rest of the limb once I'd avoided the "nasty" end.