I'm surprised other people are giving you concrete answers as it is impossible to say.

How much have you invested in building the current ROR based system?

Are the developers happy to code with both or are they simply steering you towards the technology they know?

Magento is a great platform. Extensions are a double edged sword, they can be very good and save a lot of effort. Likewise there are some terrible extensions out there. The cumulative effect of adding lots of extensions can be really bad as well.

Ultimately, you are likely to get what you pay for, no matter which platform you go with.

100% agree with Joseph. There are lots of variables here to consider. In addition to how much you've spent, there's the variables of resources for Magento vs ROR that you have, budget that you have, and time that you have.

For instance, we only recommend doing a custom solution (ROR in this case) if you have a large development budget and ample extra budget for changes and revisions, as that's custom development work, which is expensive.

If you have a very tight budget, we recommend Shopify or BigCommerce, spending very little on custom website design and investing in content (great branding, photography and blog posts) and marketing (aggressive social marketing which can be measured and optimized for growth).

Lastly, if you're in the middle on budget, we recommend doing a dedicated installation with an existing solution, such as Magento. We do highly recommend limiting the number of extensions as well, as, again, they can be great but they can also interfere with each other. Magento's technical structure is such that it is somewhat difficult and finnicky to remove plugins, so you need to be very careful with them in the first place. You'll also need to set up a staging server as well.

We've recently completed a bunch of sites on Shopify Basic and Shopify Plus (enterprise), and love Shopify moreso than Magento. We are also in the midst of trying Spree, which I've heard great things on.

Hope that helps!

Magento is on it's way to becoming the number one e-commerce engine. It is a beefy solution, but if you can use e-Bay you can use Magento if you dedicate the time to learn. There is a comprehensive user manual you can download plus 1000s of how to videos on YouTube.

Magento does need a customized hosting environment for proper optimization and load handling, which will cost more than the average mass web hosters out there.

Magento is becoming like the iOS ecosystem with an App Store where you can add a lot of 3rd party features easily. This is a very powerful aspect of Magento.

Main question you need to ask, is: "What is the real potential of my web business?" If you see a lot of sales and large gross numbers being processed, go for Magento. If this is just a hobby of yours, then just stick with the most basic infrastructure possible that does the job.

Also, keep in mind, end of 2015 Magento 2.0 is expected released and will have a lot of changes. Anything you build with it today, expect a large effort in upgrading in the future.

The advice of going with a pre-made system is sound. No one unless they have gazillions of funding builds custom web stores anymore.

ROR is a completely different code base than PHP (That which Magento runs on. I suspect what you are experiencing is that there are far more developers comfortable with PHP than there are with ROR and ROR resources can be a little more costly. That said, depending on how much work you have had done with your ROR site, and the platform you are running it on, for example if the site is actually running on a hosted solution like Shopify, there is alot less customization you can do. That said, Magento is extremly customizable, but can also be tricky to learn if you don't have a team behind you that is willing to train you or fix issues as they arise. That said to, not all extensions are compatable, so I might suggest that you find a good ROR resource to review your code and advise as to the costs to make the improvements you need, then find a reliable resource for PHP Magento and see what it would cost to rebuild there. By all means I can always assist, so let me know if you needed anything else on that.

No, you use Shopify.com and then build integrations for it. You can then sell those integrations and create more revenue streams.

I believe you do need it.
Magento as a marketplace has an organized search functionality with intuitive product categorization and collection. This way, searching for a product becomes easy.
You can read more here: https://suyati.com/blog/benefits-of-magento-as-a-marketplace-solution/
Besides if you do have any questions give me a call: https://clarity.fm/joy-brotonath