Personally, I think twitter isn't just spammy. If just spammy, your followers will annoy it and your twitter is very easy to be suspended. In my mind,firstly, before you use twitter as marketing tool, you can try to consider it as making good friendship with your followers. Try to share valuable contents with your friends and provide help so that make your friends trust you, then you can use it for marketing.
Twitter is mostly full of spam people trying to spam people into buying things and visiting their blogs. There is very few if any original content on twitter. It is just a free for all fish market where internet marketers peddle their stuff to unknown browsers and visitors.
Thing about Twitter is.. It started off as a tech thing, micheal arrington, phil cashmore, steve jobs , kevin rose there all on it.. word spreads to koby briant, paris hilton, david beckham etc... now, there is a newspaper in CA which has a whole page from celebrity twitter quotes every day :O
Im not on Twitter, I avoid knowing that once I join il be hooked and il spend many hours of my day being wasted on their.