I still love stickers, but is it too early to use Halloween stickers? Maybe, maybe not!
I also love to use washi tape. I will use it to join the sheets of paper to make a little booklet, or just use it to decorate one edge of the page. I also use it to seal envelopes even when I use wax seals, and when the envelope is a peel & stick or self-seal envelope.
In the end, it really doesn't matter whether you use a ballpoint pen or a fancy fountain pen, plain paper or decorative ones, it is the words and contents of the letter that matter the most. If embellishing a letter brings you happiness, then I'm all for it.