Sounds like a fun trip.
I do not think Budapest or Amsterdam are high on the radicals hit lists.
Places with large Muslium populations would concern me, but places that serve pork with everything like Hungary,Slovakia, Czech Republic, Germany all seem pretty safe.
Spain, France, and parts of England with large Muslium populations, if 1% are radicals and want to take out revenge, they are going to do it, they will try to hit places like Kadafi did in the 80's that get US military personell off the base, at night clubs.
I do not think postponing a trip because some looser with a grudge may attack is a reason to cancel a trip.
Their goal is to disrupt our life style, get us not to spend $ and grow our economy or the global economy making more ticked off people that blame us for their failures and join their side. If you do not go on the trip you are letting them win at terrorizing you.
Live your life, don't take unnessary risks but go live your life.
I vote go. Take lots of pictures and bring you kids and grandkids brick a brack from the different places. I still have a painted horse some where in the house my Grandpartents brought me back from one of their trips in the late 70's or early 80's from Norway. I can still see them talking about the many trips they went on so many years ago and reminds me of them, and planing and taking trips at 90 years old, both passing the following year or two.
Thanks for making me think of them.