Some time ago I wrote that Elizabeth’s love for Darcy could not bloom before she was assured of his feelings as well as that her wishes and hopes would be rewarded by a proposal.
Elinor expresses similar sentiments when she answers Marianne’s queries about Edward:
“I do not attempt to deny,” said she, “that I think very highly of him — that I greatly esteem, that I like him.”
Marianne here burst forth with indignation —
“Esteem him! Like him! Cold-hearted Elinor! Oh! worse than cold-hearted! Ashamed of being otherwise. Use those words again and I will leave the room this moment.” Elinor could not help laughing.
“Excuse me,” said she, “and be assured that I meant no offence to you, by speaking, in so quiet a way, of my own feelings. Believe them to be stronger than I have declared; believe them, in short, to be such as his merit, and the suspicion — the hope of his affection for me may warrant, without imprudence or folly. But farther than this you must not believe. I am by no means assured of his regard for me. There are moments when the extent of it seems doubtful; and till his sentiments are fully known, you cannot wonder at my wishing to avoid any encouragement of my own partiality, by believing or calling it more than it is. In my heart I feel little — scarcely any doubt of his preference. But there are other points to be considered besides his inclination. He is very far from being independent. What his mother really is we cannot know; but, from Fanny’s occasional mention of her conduct and opinions, we have never been disposed to think her amiable; and I am very much mistaken if Edward is not himself aware that there would be many difficulties in his way, if he were to wish to marry a woman who had not either a great fortune or high rank.”
Sadly, not even Elinor’s cautiousness spared her misery.
Mending My Own Pen 
Well, Marianne wasn’t spared from suffering but she learnt from her mistakes. That’s the way life is. At the end of the novel Marianne becomes more sensible and less impulsive and Elinor less sensible and more spontaneous: the blend of sense and sensibility makes them more mature.
You’re right of course, each of them needed some balance of sense and sensibility. That’s why I put the emphasis on Elinor, because Marianne’s suffering is more dramatic, while I always suffer more with Elinor’s silent torment. Her cautiousness didn’t serve her well. Not only she fell in love anyway, but also she guarded her feelings so well that Edward was unaware of it (that is if one believes him – my boyfriend called him a ‘matrimonial swindle’).