I would take the current tower aware, and redesign the entire thing.
Have an entire "raid" wing of the tower, apartments which can house your weapons, stats, or whatever to show off what you have done, gunsmith that actually does things with your weapons (you can reroll them and upgrade them to current damage just as you can through xur, but for legendaries).
Have entire areas dedicated to specific factions instead of simply just "oh yea, this new monarchy fool is chilling in the gutter where nobody even bothers going." A place that you can change the look of your guardian (or even his entire appearance). Make the bar useful instead of just housing xur on certain weekends, like add "under the table" bounties that you can complete for something in return.
Whole slew of things you could add.
Banshee actually sells rare items
Banshee actually sells legendary but twice a week and cost 7500 glimmer/per.
Rahool has a twin named Loohar that has upgraded decoding skills but cost motes.
Postmaster gives 2 random packages a week containing random loot depending on your level.
Mentors sell level specific armour
1-5 = White
6-15 = Green
16-25 = Blue
26-30 = Purple
30+ = Purple/2 Yellow
Add a new "Secret Charactor" like Xur.
Trade=Motes, Coins, Syns, Legendaries
More vault/Charactor space
20 more story missions (non-dlc)
Level selecting for raids.
Strike picking.
7 man raid/fireteam members.
Thank you ladies and gentlemen.
Edit: Thanks guys know it needs work but still.
A place where there's a public voice channel and you can watch live crucible matches and bet (IDK, glimmer or motes etc) on either alpha or bravo. In background, there's a monitor showing the leaderboards and who has the most winnings in that week.
Tower north, that big gate where xur occasionally is, could open up to a horde mode type arena. You could place bets on guardians in the arena and watch them fight whatever.
1. Dance Club
2. Jukebox
3. Training Area
4. Bathrooms!!!!
5. Sparrow racetrack with betting (for those of legal age)
And lastly
[spoiler]Disco ball[/spoiler]