Airport arrival times for EU (domestic) flights?

It depends on the airline, they set these times. It should say on your ticket or boarding card how far in advance you need to get to the gate, then you need to add some contingency time.
The time is usually longer for budget airlines than for full-service airlines.
I checked an old EasyJet boarding pass. It says "Gates will close 30 minutes before departure so please don’t be late.". But that is the time you have to be at the departure gate. You have to allow time to drop off your bags, get through security and find your gate.
In the case of EasyJet you need to check in online and print out your boarding pass before arriving at the airport.

Do not conflate the EU and the Schengen Area. There are some countries which are only members of one of these.
Munich to Barcelona and Amsterdam to Milan ARE international flights, but they are both intra-EU and intra-Schengen.

I guess that's my key question - how long does it take to get through security for flights within the EU? In the U.S. there used to be a pronounced difference between domestic & international, but now we all have to go through TSA security, so the difference isn't nearly what it used to be. I have no idea how it is within the EU - how different is the the security for intercontinental flights vs. EU/Schengen vs. domestic? And how efficient or well laid-out are the Munich & Amsterdam airports? Obviously I don't want to miss my flights, but I don't want to be overly paranoid either. Thanks!

I would say two hours. Security is tight whether you're flying within the Schengen area or not, and you will still have your passport checked when you are flying. Munich airport has a really annoying design where each small group of gates has only a couple of passport desks to serve it specifically, and the queues can get very long, especially if there also happens to be a flight to a non-EU country (coughTurkeycough) departing from another gate served by the same passport desks.

My understanding is that many European airlines want bags checked an hour prior to departure. So I'd allow at least 90 minutes. Like any US airport, security lines can vary depending on time of day, season and competency of the airport management and security personnel. I would not push as close as an hour and personally would allow for 2 hours.

Some airlines will shut down the baggage check desk 60 minutes before the flight so that the same people go out to the gate to work that end. 90 minutes is a minimum and 120 minutes is better.

Munich was my home airport for many years and I traveled about 2x per month for work to other locations in the EU. I always arrived 60 min before departure with never a problem. 120 minutes is too much for MUC.

DJ

It seems you like risk.

There are so many things that can throw a delay, from slow staff to multiple flights simultaneously to delays reaching the respective airport, to machines (maybe security, maybe luggage) breaking down.

I don't like risk as much as you. I always leave 2 hours for intra-Europe and an extra hour for flights to North America - regardless of airport.

I would say you can leave it as close as you like as long as you are content with missing the flight and buying a ticket on the next one.

Strait from Vueling's website:
Passengers must arrive at the airport in sufficient time with respect to the scheduled departure of their flight in order to complete all official formalities and, where applicable, check in their luggage. The check-in desks open two hours before, and close 40 minutes before, scheduled departure (even if the flight is delayed).

120 is the absolute earliest you could conceivable check you luggage which means there are people that arrive with less than 120mins to spare and will still make the flight,you can be one of those people. If 60 minutes is too close for comfort and you want to play it safe, 80-90 minutes would be fine.

MUC security is very efficient and I've never had a long wait there (less than 10 minutes). I can't speak for the other airports you list.

DJ

Okay, thanks everyone. Sounds like it's fairly similar to U.S. airports, maybe slightly more efficient. 60 minutes is too little time, 90-120 minutes should be the goal, and anything more than that is a waste since I can't check my bags earlier than that. Thanks!

I don't know about Vueling but with EasyJet you buy your hold luggage when you buy your ticket, or up to some time (I think the day before departure or perhaps some number of hours prior to travel) before departure. That's when it is cheapest. If you buy it after the cutoff it gets more expensive, and if you have to check a bag because of size or weight - they check very carefully - it becomes very expensive.

Using the EasyJet app makes checking in and making any changes very easy.

Remember that EasyJet is one and only one piece of cabin luggage, and it has to be put in the overhead bins wheels first, not sideways. No purse, laptop bag, or man bag as any sort of a "personal item". They don't do that. If you turn up at the gate with a carry on and a personal item, either you carry on the personal item and pay gate check for the now hold luggage, or you find a way for the personal item to go inside the carry on without exceeding the sizing box for the carry on. They are strict about that.

That said, when you play by their rules it is a very comfortable (for short haul) aircraft and I have never had a bad flight with them.