Wiki needs your help?

Not significantly. Though bandwidth is a major cost of running the Wikimedia sites (including Wikipedia), there's more money in servers (which have to be periodically replaced) and software development (a few developers are hired full-time to develop the MediaWiki software and extensions thereof, et cetera).

Most of Wikipedia's servers and software are already using extensive caching, both server-side (servers cache rendered versions of pages to reduce needed rendering time) and client-side (most of the data used to display a Wikipedia page is only re-downloaded every 30 days or so unless something forces an earlier refresh). Using third-party caches would save some bandwidth, but a tiny donation (e.g. $5) would be much more effective in most practical cases—not to mention that cached versions will often be out of date.

There is no reason to try to "help" Wikipedia with bandwidth conservation. The site only costs about $1.2 million annually to host and serve up plenty of bandwidth. Yet, they rake in over $7 million from donors who think it costs that much to run the website. The website practically runs itself. Your money is going to pay people who don't do their jobs well, and to fill up a savings account in the bank -- literally, to the tune of about $2 million per year.

in theory it would but the number of people you would need in order to actually make a sizable difference would be too large to comprehend.

It would be better if Wikipedia does that.