With a 3 inch level, your full droop is now 3 inches lower than it was before the spacer was installed, if you haven't upgraded your UCAs you are probably running out of articulation in the balljoint before you hit full droop. You wont hit the spring, but that's not a good thing because the upper control arm's balljoint is now what's limiting your suspension travel, putting all the tension there instead. there's a good chance that with 3" of extra downward travel, if you have never had issues it is because you have either never hit full droop with any real force, you've run out of articulation in the balljoint and are just lucky, or you are hitting the spring and didnt notice because the stock UCAs are made of a plastic that doesnt transfer sound that well.
Preload spacers are better for this (they have their own drawbacks though) the overall length of the strut does not change, what they do is sit your ride height higher in the normal range of travel., meaning that your UCAs are less impacted, and there is no downward overtravel. downside to pre-load spacers is this eats some of the upward travel and increases the spring rate leading to a rougher ride.
Bilsteins on the other hand move the spring perch up, rather than increasing the spring rate with a pre-load, mitigating the rougher ride characteristics of a spring spacer, and mitigating the overtravel issues with top hat spacers, since the strut's overall length has not changed.
bilsteins are definitely the best option for retaining stock ride characteristics, and protecting the balljoints and UCAs from damaging downward overtravel.
i'm relativerly new to this, so if anyone sees glaring issues with what i've said here, feel free to correct me. this is how I understand it at this point.