Since I play Mechwarrior Onlie too, I would like to show that MWO bonus system is very nice and balanced.
All bonuses are very small (like +1% to torso twist, -10% to breaking distance). Additionally you get your main account experience and can buy specific weapon range/reload buffs or special abilitites (seismic sensor pinpointing mech location on mech moves on your radar is pretty sweet).
You get a coule skills to unlock at 3 tiers of mech mastery: basic, advanced and elite - mech specific. In order to get it to elite you need to get 3 mechs of same chassis unlocked at basic or advanced. It takes a lot of time, so as a casual it took me a year to fully develop a community warfare 4-Clan, 250-tonnes lance, fully upgraded. It was very rewarding to watch it grow.
Hawken has internals and items you can put on any mech + pilot and mech progression with no specific rewards. Giving each mech a 1 mech slot + 1 pilot slot would be interesting. It would surely make new players more keen on sticking around with some prize at the horizon, specifically for pilot lvl 30 and lvl 6 mech. But the bonuses should be some fairly basic buffs.
+ An idea how to make it actually work and help balancing issues:
Give each new player a temporary skill for dmg reduction when receiving damage from lvl 30 players. The bonus scales down as the player progresses, until unlock at lvl 30 with several active skills to choose from + mech specific unlocks at lvl 6?
Keep in mind making a change of the skill kind of a fuss, thus making changes in match impossible (hourly cooldown?).
Blocking using certain skills on certain mechs for balancing purposes would be interesting too (no speed buff for A class, no armor buff for C class?).
So... How about at least a dedicated testing server where the abovementioned handicap for lvl 30 players is in order?