Yeah, mirrors look great and will make your space look bigger (if you can stand the shock of continually surprising someone who looks just like you wandering around your garden ...). But, the larger the mirror, the more likely birds are to fly into it, with sad consequences.
Personally, I'd go for the perspective tricks ... plus, an old artist's trick: "warm" colours (reds, pinks, oranges) "jump", while "cool" ones (blues, mauves, whites) are recessive. So design your garden with blues in the distance and hotter colours near the house.