Someone with more sPvP knowledge will be able to confirm but I don't believe it nets you any XP. You're upleveled and have access to everything. Only thing you'll gain is PvP ranks.
WvW also uplevels you but does not unlock everything and you gain XP. Its more an extension of PvE than straight up PvP and the maps count toward character map completion (which a ton of PvE only people complain about). However, as an upleveled person in WvW, make sure you keep updating your armor as you level. If you're still rocking the starter armor and have reached level 30, you'll probably be dying quickly in WvW. I generally keep a character out of WvW until I've unlocked the skill bars (elite unlocks at level 30). The lack of traits and top armors will already make you weaker so don't expect to frontline a zerg with a low level untraited character. EB is quicker and safer than BL for leveling imo too. You'll get items from kills so you can probably keep armor near max level with your drops.
And just an fyi, canons in WvW are effing awesome. If you're defending in a keep with canons (its an upgrade so they won't always be there), man a cannon if no one else is on it. It does a lot of damage and you'll tag a ton of guys for XP/bags. Another server was attempting to take out our trebs at our Eternal Battlegroups (EB) keep and I had at least 12 bags drop within 10s shooting at the middle of the zerg with a canon.
If we have nothing in SBI BL and there is a zerg starting to get everything, it is good exp. 1 exp bar for a tower and 2 exp bar for a keep.