You should absolutely consider spikes, or better yet, outriggers. (oregondv.com) This should really help you achieve what you are looking for.
improving bass on large floorstanders....
I have some 3 way tower speakers that could use some bass improvement...however...if the results are minimal...i probably will pass...at any rate...would the addition of floor spikes or possibly a cable change be the answer?...I am looking for tighter, leaner bass if possible...thinking entry DH labs or Nordost...at any rates...what has worked/ not worked for others?