Ditto to Rob's comments. I have many older rock/pop LPs that just aren't recorded very well. Many of those have a rolled-off, congested sound, like you describe. OTOH, some of my older LPs sound very good. So, do make sure you try a variety of LPs, and maybe try some audiophile-type pressings, before drawing final conclusions. BTW, to me, one of the virtues of vinyl that seems to come through regardless of the overall quality of the recording is that the contours of notes, how they rise and fall, sounds natural.
Other than that, VTA is definitely something to play with, as Spooky suggested. The core of my TT is an old Planar 3 like yours. It came with a thick-ish (maybe 3/16") felt mat. I switched to a thinner felt mat, which definitely opened things up. (I use a different mat now, but there's nothing wrong with felt, and you may be able to find a thinner one for little or no money.) Also, putting my Planar 3 on a good vibration control device also made a significant difference in openness and clarity. This is running into real money, but probably less than stepping up in the level of cartridge or tonearm you have.
Best of luck!
Other than that, VTA is definitely something to play with, as Spooky suggested. The core of my TT is an old Planar 3 like yours. It came with a thick-ish (maybe 3/16") felt mat. I switched to a thinner felt mat, which definitely opened things up. (I use a different mat now, but there's nothing wrong with felt, and you may be able to find a thinner one for little or no money.) Also, putting my Planar 3 on a good vibration control device also made a significant difference in openness and clarity. This is running into real money, but probably less than stepping up in the level of cartridge or tonearm you have.
Best of luck!