It's actually probably more useful to have the big radars in Europe, for anything not specifically targeting that piece of the continent. Hitting a ballistic missile during boost phase is
difficult, especially one launched by the US, Russia, or China, who are willing to pay for more and better ABM countermeasures on their launch vehicles. Having forward radars to detect and track the launch makes it easier to hit later.
It also makes it easier to estimate the target area for each vehicle, and assign priorities accordingly.
The US and best buddy Israel have developed some incredible anti-missile and anti-artillery technologies [0][1]. While really expensive, they do ensure that a very clear and obvious act of war has to occur in order to seriously damage a defended area. A handful of guys with plausible deniability can no longer just fire some rockets and mortars over the border and expect to get away, to do it again later. The projectiles that might have killed someone are destroyed in midair, and return fire is already incoming to the original firing positions.
It is possible that the US has fielded systems on its own that are at least an order of magnitude more expensive than those shared with Israel and Europe, but are not known to have been tested by live fire, because of the increased difficulty and expense in firing missiles that can hit US territory. Iron Dome protects cities and towns. Whatever the US has probably protects whole states, if not the entire continent. The military certainly isn't spending all 3% of the whole US economy on individual soldier benefits. And not everything produces as much disappointment as the F-35. Sometimes the big expensive thing actually works as intended.
Telemetry stations in Europe are not necessary, but they are cheaper to operate than the alternatives. And they provide the PR benefit of, "Oh yeah, I guess we can provide first-strike deterrence for your country a little bit too, while we're at it."
You need only look at the recent history of the Crimean peninsula to know that your country has to have some strategic importance to the US in order for the American military (or diplomatic corps) to even attempt to defend it. The more recent additions to NATO would be wise to see to their own defenses, under the presumption that NATO is far more able to avenge than protect.
[0] https://en.wikipedia.org/wiki/Iron_Dome
[1] https://en.wikipedia.org/wiki/Arrow_3