I have received (almost) nothing but excellent treatment by waiters in Venice when I try to speak Italian. In my experience, no real Italian will treat someone trying to speak their language badly. They will usually be thrilled. I did have one experience from a very brusque waiter in the area several blocks past the Rialto bridge.
Every time I started in Italian he would interrupt me in English (he did this to other people who were French trying to speak Italian by interrupting them in French). Finally when he saw my name on the credit card he said my name was the same as that of his mother. He said he was Russian, but born in Houston.
With the EU and the need for people in the tourist industry to speak English and other languages, increasingly you will not get native speakers at many restaurants. So don't automatically blame the Italians or French or whoever for being unpleasant. I was at a wonderful restaurant near the Metropole last night (De Leoni) and everyone spoke Italian to me and it was clear that all of them were native speakers. BTW great restaurant!
I had been somewhat quick to judge it as anti-American feeling in the past but I think it is more likely that many of the people who work in the tourist industry in Europe nowadays are from elsewhere and find it easier to speak English.
Could it be that you are underselling yourself as little?
Talking only of the UK for a moment, I am always very conscious of how few of our tourists (including me, too often) even bother to try to speak another, local, language. As you point out, on many occasions, it may be totally impractical, but just trying does help to dispel some of the appearance of post-colonial self-centredness of which we can still be guilty.
Another small point to add to your assessment. Such is the importance attributed to devloping English-speaking competence through much of Western Europe, many younger people - students, waiters and the like - welcome the opportunity to practice their linguistic skills with you. In fact, persuading them to speak Italian, Dutch or Spain can be very difficult.
In France it happens to me all the time when people (esp. young as you say) want to use their English. If they are students or others eager to practice, I'll go along. But at least in France I'm fluent and want to speak French. My Italian was self-taught, so it's pigeon Italian (useful in Venice:) ), but I find Italian waiters at nice restaurants will go out of their way to let you try it on them and will even compliment you. I've found so often that you can get to know another culture so much more if you know at least a little of the language.
I felt utterly lost linguistically in Spain since I don't speak Spanish and many people in Andalusia didn't speak English. Italian worked some of the time.
What I have always noticed, however, is that when faced with a cheerful person willing to let me try I can speak much more easily. With a brusque person, I start stumbling over my words (or here) speak French by mistake. A former German prof told me that the mind works that way. If you know one foreign language well and know a little bit of another, you'll tend to default to your first foreign language rather than English when you don't know a word. Leads to some amusing polyglot!