Honestly I don't think they need to. With the group of TEs coming back, Pitta, Williams, Gilmore, Waller and Bolye, I think the Ravens should have a good shot at finding the best 3 maybe 4 of those guys to provide really strong 2TE sets. They can more than cover the possession chain moving aspect of the offense.
As far as WR, I think Wallace has done more than enough to grant him an extension. Sign him to a 3yr deal and lower that 8Mil against the cap. I am more than comfortable with the combination of Perriman and Aiken handling the other outside spot opposite Wallace. Perriman should be ready to take over that starting position imo, even if he's not a true #1 yet and if not you have Aiken to help out. Not saying Aiken is #1 caliber but he's definitely good enough to keep the offense moving while guys like Wallace and Perriman make the big plays. I also think this offseason is the prefect time to develop guys like Moore, Camp and even Kenny Bell or Keenan Reynolds on the PS.
You just can't consistently get your 4th and 5th WRs involved in the game plan and that really hurts their development. So if you bring in a veteran i'm assuming you're bringing someone in who can start opposite Wallace because otherwise Aiken is a veteran reserve. So that vet along with Wallace would take the majority of reps at WR and push Perriman, Aiken, Moore and Camp further down the depth chart. There is always veteran guys hanging out around camp time waiting to get signed by a team late. I say go into camp with Wallace and Aiken as your veteran and use the entire offseason and camp to develop Perriman, Moore, Camp, Reynolds and Bell.
The only way I want another veteran added is if SSS decides to come back and even than I don't want him seeing as many snaps over Perriman.