My attitude is that email is a system of sending messages quickly and conveniently and not a work of art or graphics demonstration in its own right. My email setups and those of most, if not all, businesses and a lot of home systems are set to receive emails in plain text so, however much time and effort you may have spent creating some fancy parts to your message, it gets wasted or lands here as a piece of html code which few are going to bother to open or decipher, most certainly I wouldn't.
Remember that email is the most common method by which viruses are propagated nowadays and the more complex and arty the message, the easier it may be to hide these nasties.
The file sizes, as you realise, are much larger with all the padding of the graphics and if your recipient has a restricted size mailbox (as per most free web based systems), it won't take much to fill it up.
For filtering your mail, use something like MailWasher which has been promoted a number of times on here.