I've had a Brother Innovis NQ900 for several years now, and for me it was a worthwhile investment. It was a major upgrade from my basic Singer. I understand your uncertainty because I also thought the NQ900 might be too much machine for my needs and skill level. Then once I started sewing with it at home I realized it made a world of difference. It made sewing so much easier and more enjoyable. I sew quilts, garments, home decor, small bags- some layers, denim, canvas. The NQ900 has good throat space, nice smooth stitch quality, plenty of features, an extension table- it's really nice. I agree with others who said get the best machine you can afford- you'll enjoy sewing a lot more than if struggling to sew everything on a lower level machine. If you can get the NQ900 at a great price it's probably worth it even for a beginner since it gives you a better chance to succeed and have fun.
That said, I ended up eventually getting a Juki TL-2010Q, too- which I love and use for most of my sewing. Originally I got it for quilting but it ended up as my primary machine. If you like sewing bags and thick layers- a semi-industrial straight stitch machine like this Juki is ideal. It's great for all kinds of sewing, as long as it's straight stitch (or free motion quilting). It's smooth, powerful, and simple. One thing I love is the visibility- the Juki's design lets me see what I'm doing much better than on the Brother (or most regular multi-stitch machines, which are kind of low and bulky). I got a 1/4" foot for quilt piecing and do all my piecing on the Juki. But I use the NQ900 to attach binding, and often use a blanket stitch or decorative stitch for fun on the binding. Since the Juki is straight-stitch only, I use my NQ900 for buttonholes, zig-zag and specialty stitches, applique, etc.
One option- if it's in your budget- keep the small Brother you have, use it for buttonholes, zig-zags, etc., and get a semi-industrial Juki like the TL2010Q as your main machine. My Juki was half the price of the NQ900. If you can try out the Juki TL2010Q or a similar machine (other brands make their own versions) in a shop, along with the NQ900, with your fabrics, that will help you decide. Having two machines probably seems like a lot for a beginner, but they're like a team. If you do tons of specialty decorative stitching, or you really don't want two machines, you might prefer the NQ900. But if you do mostly straight stitching, quilting, and heavy duty (bags/thick layers), the Juki is ideal, and you'd only need a small multi-stitch machine on the side for the specialty stitches. I just want to put that idea out there in case you want to keep your small Brother machine, and when you can afford it, add a heavy duty Juki (or comparable semi-industrial straight stitch machine). Good luck on whatever you decide to do!