Alternative to shutters
Suggestions:

Paint the shutters. You say that the shutters you have are faded gray, and that's not going to add much interest to your windows. I think almost any color would be better than that. Black or white would be good if you want something that stands out more, but is still very traditional in appearance. If you want actual color, a muted red, green or blue can work without calling too much attention to itself. (Or go with a non-muted color. There's no HOA to tell you no.)

Add a trellis with a climbing plant. This can provide some visual interest, and most climbing plants are fast growers because they don't need to support themselves. (They can't do much to brick that's in good condition, but if your brick is just a facade, or if the mortar is crumbling a bit, I'd skip this.)

Add window boxes with flowers. These can also be painted to add a splash of color, on top of the flowers during the appropriate part of the year.

Add architectural foam trim to the windows. There's a lot of options here, but I suggest not going overboard; it's easy to end up cheap and tacky.