IMO, 3 showers for the same bride is ridiculous!
Never mind the 'one shower per guest rule', to me the rule is 'one shower per bride'!
Personally I'd rather see 3 small showers as described by the OP, than one giant extravaganza with 50-60 people.
I agree, especially if it involves three separate groups of people with little or no overlap.
So do I.
I don't think that hard and fast rules are a great idea for this. A sister or best friend might actually like to be included in everything. Other times, people get invited as a courtesy when they won't be able to attend -- e.g. Grandma who lives far away. No big deal to get more than one of those.
Ditto whether a guest should buy more than one shower gift if invited to more than one shower (I state this from the guests' perspective, not the bride's, because she should not be feeling entitled to even one gift, let alone multiples). I think it just depends on your relationship
to the bride, and if you are invited to more than one shower, unless it's due to a coincidence like being both, say, a cousin and a classmate, you are probably very close to the bride and/or the hosts. I don't think you're obligated
to buy multiple shower gifts in any case.
Personally, I probably would bring some kind of gift to every shower I attended, although they would probably be much smaller gifts, even for a bride I'm very close to. In addition to thinking of the bride, I also want to cooperate with what the hosts have planned, and I want their shower to succeed. Anyway, if it's to be a small gift, because I am attending multiple showers, it probably isn't very much more than I would have spent on a hostess gift if it had been some other kind of party.
The one thing I wouldn't do -- and I know that not everyone feels this way! -- is bring a greeting card but no gift. I'm not a big fan of greeting cards anyway, but I do sometimes use them. To me, though, they are simply stationery or gift enclosures. Yes, of course, a heartfelt note isn't worthless; indeed, it's priceless. But to bring it to a shower and hand it to someone -- or have her open it during the shower? -- seems odd to me. I mean, I would think that even those who do consider a greeting card a "gift" would agree that not every gift, even every great gift, is a good choice for a shower (a massage, for example!). A letter is something you send someone, and it's personal, between the two of you; writing it on a printed greeting card doesn't change that, in my opinion. A printed greeting card with little or nothing more than a signature -- well, actually, to me that is almost worthless; certainly not a nice gift. If I weren't going to bring even a token gift, because I had already given (or will be giving) a substantial gift at another shower, I would just bring nothing.