"Getting that spacey lydian sound" is more than just using the lydian scale over any old chord progression. The harmony helps to dictate what scale to use and what the scale will sound like. If you play F Lydian over a 1, 4, 5 in C, it's going to sound just like C Ionian. You need the right chords to play over to get that sound... Satch's "Flying in a Blue Dream", for example, is a camp from C to D to C. The key is G Major, with the tonal center being a C, so voila, C Lydian is the scale of choice, and you really get that lydian sound out of it.

You want to get a Mixolydian sound? Playing D Mixolydian over G, D, Em, C won't do it, no that's G Major key with a G tonal center. However, if you play D, C, G, G, you can use the D Mixolydian because of harmony makes it sound right.