Limping is a problem because a lot of loos players will limp with anything that they have(93o), it's cheep and if they are so lucky to hit flop 9-A-3 they will make strong hand and next move it will be all-in against any bet.
So limping is not options.
But, what to do with speculative hands when you faced with raising in front of you. That is right question if you ask me.
For speculative hands, as mention in the post, I use a rule 3-6 and 5-10, which I read in Kill Everyone by Lee Nelson. The rule is the following.
The Rule 3-6:
Low suited connectors (32s-T9s), Low suited one-gapers (75s-J9s) and Low suited aces (A2s-A9s) I will pay max 3-6% of my stack. And if I hit the trips on flop with 3s or some good drew you have chance to beat someone who can't resist to his love with KK or AA and take all his stack.
If I am in MP and I faced with raise I will pay 3% of my stack and in LP I will pay to 6% max. Everything between depends how much you like your hand and reading of your opponents, everything above is fold.
The Rule 5-10:
This rule I use for Low pocket pairs (22-88). Same thing like in rule 3-6 just other percentage of use and it is 5 to 10% of your stack. If you hit a set it will likely win you big pots.
Also, there is rule "Call 20" and that is to be sure that you and your opponents have big enough stack to make the call worthwhile. If you and opponents have 20 times the raise amount in your stacks, the call is worthwhile and go for it.
It is very effective at the beginning of the game, they all have a big stack and with small investment you can make a big hit. Also, that will confuse your opponents when you make same raise or call of raise with monster hand.