Yes and no. In some circumstances I agree with you, in other circumstances I think you have it backward.
I shall enumerate some cases (note that US citizens always count as "inside the US" in this case breakdown):
* inside the US, old-school warrant exists
* inside the US, secret warrant exists
* inside the US, no legal authority
* outside the US, no legal authority
* outside the US, weird US-logic legal authority
1) If you're inside the US, and the cops have a non-gag-order warrant, you're no safer with your own server. With your server, they serve you, you know about it; with gmail, they serve Google, and Google tells you about it. No difference.
2) If you're inside the US, and they use a secret warrant, in this case your own server might be better. They can probably still do something tricky to you, without you knowing, but using GMail makes it slightly easier for them to get your information without your knowledge.
3) If you're inside the US, and they have no legal authority, then you're fine in both cases. Unless they break into your server illegally. In this case, their job will be orders of magnitude easier if you run your own server.
4) If you're outside the US, and they have no legal authority at all, same as the previous point: if they try to break in, their job will be orders of magnitude easier if you run your own server.
5) If you're outside the US, they might get FISA clearance to get your stuff. In this case, I think you're better off with your own server. This is comparing Google's legal pushback vs breaking into your server. It's totally possible that breaking into your server is orders of magnitude harder than convincing Google that they have legal authority.
In an ideal world, this last case would only apply to political enemies of the US. You'd be able to figure out for yourself if it applied to you, and act accordingly. What kind of idiot uses a US company to plan terrorist attacks on US interests, amirite? Or to leak things to wikileaks (categorize that however you like). But what is much much less clear is whether the US does in fact use this type of surveillance to unethically benefit US corporations, for example. We've heard unsubstantiated accusations to that effect; nothing in my life experience helps me to know if I do or do not live in that kind of world.